9 th International Conference on Hydrodynamics October 11-15, 2010 Shanghai, China 97 Energy gradient method for turbulent transition with consideration of effect of disturbance frequency Hua-shu Dou 1* , Boo Cheong Khoo 2 1 Temasek Laboratories, National University of Singapore, Singapore 117411 2 Department of Mechanical Engineering, National University of Singapore, Singapore 119260 *Email: [email protected]; [email protected]ABSTRACT: The energy gradient theory for flow instability and turbulent transition was proposed in our previous work. It was shown that the disturbance amplitude required for turbulent transition is inversely proportional to Re, which is in agreement with the experiments. In present study, the energy gradient theory is extended to include the effect of disturbance frequency on turbulent transition. The theoretical result obtained accords well with the experimental data in literature. KEY WORDS: Turbulent Transition; Energy gradient method; Disturbance amplitude; Disturbance frequency. Capturing the process of wave to runup K. M. Mok * , Jie-lin Lu, K. I. Hoi Department of Civil and Environmental Engineering, University of Macau Av. Padre Tomás Pereira, Taipa, Macau SAR, China * E-mail: [email protected]ABSTRACT: Four types of wave to runup transition processes were examined by using a high speed video camera capable of capturing 490 frames per second. The present investigation was set out to capture the missing details reported in previous study using only 30 frames per second recording rate. Through examining the wave to runup transition processes of different incoming waves with offshore Froude number ranging from 1.08 to 1.49, it was found that the main features of the four types of transition process were consistent to those described in [1]. The non-overturning process of the upper part of the wave front occurring in the collapsing type was confirmed. The water indeed shot out from the bottom to initiate the runup process on the dry beach. However, observations in the present study also suggested that there could be an in-between transition mode existing between the plunging type and collapsing type; i.e. the upper part of the wave front may overturn onto the shot-out wave toe before touching the dry beach. Further research is recommended. KEY WORDS: Surface waves, runup; shoaling; wave transformation Generation of long waves in ice-covered lakes by moving disturbances of atmospheric pressure Izolda V. Sturova Lavrentyev Institute of Hydrodynamics of SB RAS Novosibirsk, Russia E-mail: [email protected]ABSTRACT: The effect of ice cover on the oscillations of water in a two-dimensional constant-depth basin within the linear theory of long waves is considered. The ice cover is treated as thin elastic plate in the presence of compressive force. The ice is fastened hardly to a shore. The eigenfrequencies and eigenfunctions of free oscillations (seishes) are obtained. The forced oscillations of fluid and ice cover under the action of a
Transcript
9th International Conference on Hydrodynamics October 11-15, 2010 Shanghai, China
97
Energy gradient method for turbulent transition with consideration of effect of disturbance frequency
Hua-shu Dou 1*, Boo Cheong Khoo2
1Temasek Laboratories, National University of Singapore, Singapore 117411 2Department of Mechanical Engineering, National University of Singapore, Singapore 119260
ABSTRACT: The energy gradient theory for flow instability and turbulent transition was proposed in our previous work. It was shown that the disturbance amplitude required for turbulent transition is inversely proportional to Re, which is in agreement with the experiments. In present study, the energy gradient theory is extended to include the effect of disturbance frequency on turbulent transition. The theoretical result obtained accords well with the experimental data in literature. KEY WORDS: Turbulent Transition; Energy gradient method; Disturbance amplitude; Disturbance frequency.
Capturing the process of wave to runup
K. M. Mok *, Jie-lin Lu, K. I. Hoi
Department of Civil and Environmental Engineering, University of Macau Av. Padre Tomás Pereira, Taipa, Macau SAR, China
ABSTRACT: Four types of wave to runup transition processes were examined by using a high speed video camera capable of capturing 490 frames per second. The present investigation was set out to capture the missing details reported in previous study using only 30 frames per second recording rate. Through examining the wave to runup transition processes of different incoming waves with offshore Froude number ranging from 1.08 to 1.49, it was found that the main features of the four types of transition process were consistent to those described in [1]. The non-overturning process of the upper part of the wave front occurring in the collapsing type was confirmed. The water indeed shot out from the bottom to initiate the runup process on the dry beach. However, observations in the present study also suggested that there could be an in-between transition mode existing between the plunging type and collapsing type; i.e. the upper part of the wave front may overturn onto the shot-out wave toe before touching the dry beach. Further research is recommended. KEY WORDS: Surface waves, runup; shoaling; wave transformation
Generation of long waves in ice-covered lakes by moving disturbances of atmospheric pressure
Izolda V. Sturova
Lavrentyev Institute of Hydrodynamics of SB RAS Novosibirsk, Russia
E-mail: [email protected] ABSTRACT: The effect of ice cover on the oscillations of water in a two-dimensional constant-depth basin within the linear theory of long waves is considered. The ice cover is treated as thin elastic plate in the presence of compressive force. The ice is fastened hardly to a shore. The eigenfrequencies and eigenfunctions of free oscillations (seishes) are obtained. The forced oscillations of fluid and ice cover under the action of a
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moving disturbance of atmospheric pressure are investigated. The input data are taken to have values typical of Lake Baikal. The time dependence of total mechanical energy of the fluid is calculated for different velocities of pressure motion. The variations in ice-bending stresses are determined and the causes of shore-ice breaking are explained.
Surface and interfacial gravity waves due to a disturbance
steadily moving in a two-layer inviscid fluid
Dong-qiang Lu *, Shi-qiang Dai 1 Shanghai Institute of Applied Mathematics and Mechanics, Shanghai University, Shanghai, China 2 Shanghai Key Laboratory of Mechanics in Energy and Environment Engineering, Shanghai, China
ABSTRACT: The generation and interaction of surface and interfacial gravity waves due to an submerged source moving in a two-layer fluid are investigated analytically for two-dimensional cases. The fluid is assumed to be inviscid and incompressible. The density of each of the two layers is constant. Two different boundary conditions are considered for the upper surface. The upper fluid of finite depth is bounded above by a rigid lid or a free surface. Based on the assumption of small-amplitude waves, a linear system is established. The integral solutions for the free-surface and interfacial elevations are obtained by means of the Fourier transform. Then the corresponding asymptotic representations are derived for far-field waves by the residue theorem. The critical Froude numbers for the existence of far-field waves are derived for the two-layer system bounded above by a rigid lid or a free surface. The effect of different upper boundary conditions on the wave generation are discussed. KEY WORDS: Two-layer fluid, simple source, surface and interfacial waves, asymptotic analysis
Coherent vortical structures and methods of their control for drag reduction of bodies
V. V. Babenko 1*, H. H. Chun 2 , Inwon Lee 2 1 Institute of Hydromechanics National Academy of Sciences of Ukraine, Ukraine,
*E-mail: [email protected] 2 Pusan National University, Advanced Ship Engineering Research Center,Korea,
ABSTRACT: Now the increasing attention is given researches to effective methods of drag reduction. It is revealed, that, in particular, in a boundary layer all power exchanges are caused by features of separate kinds of coherent vortical structures. The analysis is carried out and ordering of the basic types of the coherent vortical structures arising at movement of bodies in real conditions is executed. Classification of coherent vortical structures and methods of their control in a boundary layer are developed depending on their intensity. The method of susceptibility is developed by a boundary layer of various disturbances. Some kinds of the combined method of drag reduction are resulted. The executed researches of physical features of resistance of friction control are checked up at an experimental research of integrated characteristics on various models axis symmetric bodies. KEY WORDS: Drag reduction, susceptibility, coherent vortical structures and combined methods.
On stability of MHD flows located on the surface of axisymmetric torus
Boris A. Lugovtsov 1, Maria S. Kotelnikova 1,2* 1Lavrentyev Institute of Hydrodynamics,
2Novosibirsk State University, Novosibirsk, Russia
ABSTRACT: We consider the problem of the evolution of azimuthal perturbations (spontaneous swirling) in axisymmetric magnetohydrodynamic flows of an ideally conducting fluid with circular streamlines. The fluid is in a toroidal gap between two surfaces with constant values of the stream function. The equations of fluid motion are derived in the approximation of narrow gap. The parameters at which spontaneous swirling is possible are determined numerically, and the properties of secondary swirling flows resulting from instability of the initial steady-state poloidal flow are established. It is shown that for certain parameters of the initial poloidal flow, the energy of the initial flow is almost completely converted to the energy of the azimuthal (rotational) velocity field and magnetic field that arise. In this case, over a wide range of parameters of the initial flow, the time-averaged energies of the rotational motion and magnetic field take identical values for large t. We note that even for a small degree of magnetization, instability can give rise to a considerable magnetic field, which can be treated as the spontaneous occurrence of a magnetic field due to extension of the force lines of the initial weak poloidal magnetic field. The numerical studies of spontaneous swirling revealed some properties of the secondary flow, which is irregular (chaotic) in time and its spatial structure is rather complex with the presence of differential rotation, which is a consequence of the conservation laws for the angular momentum and azimuthal magnetic flux. KEY WORDS: MHD flows; swirling; narrow gap; stability.
A new perturbation solution of groundwater table fluctuations in tidal beaches
Yu-qiang Xia.1, 2, *, Hai-long Li 3, 1, Michel C Boufadel 2
1School of Environmental Studies & (MOE) Biogeology and Environmental Geology Lab, China University of Geosciences, Wuhan, China
2Department of Civil and Environmental Engineering, Temple University, Philadelphia, PA, USA
3School of Water Resources and Environmental Science, China University of Geosciences-Beijing, Beijing, China
* E-mail: [email protected] ; [email protected] ABSTRACT: This paper modeled tide-induced groundwater flow in a vertical beach with a thin submarine outlet-capping. By implementing a perturbation method based on the Boussinesq’s equation, a new approximate solution was derived for the model. Then the solution was compared with previous analytical solutions derived from the linearized Boussinesq’s equation. The results showed that the error between the present and previous solutions increases with the value of the ratio of tidal amplitude to the aquifer’s depth below the mean sea level and the leakage of the submarine outlet-capping. KEY WORDS: Perturbation solution; water table fluctuation; tidal effect; submarine outlet-capping; tidal beach.
Bifurcation behavior of laminar flows of a boundary layer problem
Chun-qing Lu
Department of Mathematics and Statistics, Southern Illinois University Edwardsville
ABSTRACT: This paper presents a theoretical analysis on the bifurcation behavior of solutions to a nonlinear equation ''' '' 0f ff− = with boundary conditions: (0) ,f C= (0)f ξ′ = and '( ) 1f ∞ = where ξ and C are parameters. It shows that if 0ξ ≥ including the case 1ξ ≥ , then for any C the boundary value problem has at most one solution. However, for any 0ξ < , there exist some C 0< such that the boundary value problem admits at least two solutions. KEY WORDS: Laminar flows, Bifurcation, Boundary Value Problem, Plasius equation.
On transmission of pressure across thermocline to ocean bottom
Jia-chun Le
Shanghai Institute of Applied Mathematics and Mechanics, Shanghai University Shanghai, China
E-mail: [email protected] ABSTRACT: A direct route for pressure transmission from free surface to ocean bottom is discussed. The ocean is of infinite horizontal extent, the vertical sound profile is composed of three layers: in the upper (mixing) layer the sound velocity is constant, in the intermediate (thermocline) layer the sound velocity decreases exponentially with the depth, and in the lower layer the sound velocity increases linearly with the depth. Equations with easily found closed-form solutions are obtained, and the pressure at the bottom depends upon the sound profile rather than the depth, therefore the effect of free surface may not die out. KEY WORDS: Microseism; pressure; waves; thermocline; ocean acoustics.
Flexural-gravity waves due to unsteady motion of point source under a floating plate in fluid of finite depth
Alexandra V. Pogorelova*, Victor M. Kozin
Institute of Machining and Metallurgy Far Eastern Branch of the Russian Academy of Sciences Komsomol’sk-on-Amur, Russia
ABSTRACT: The paper deals with the theoretical investigation of the straight unsteady motion of a point source submerged into the liquid of finite depth below the floating ice plate. The formulae describing the plate deflection and obtained with the help of integral and asymptotic methods are numerically analyzed with respect to velocity and submergence depth of point source, basin depth, ice plate thickness and Young’s modulus. KEY WORDS: Submerged point source motion; floating plate; vertical deflection; flexural-gravity wave
Study of wave induced radiation stress and vertical mixing in the Yellow River runoff diffusion
Bing-chen Liang, Hua-jun Li, Jing Zhang 1* 1 College of Engineering, Ocean University of China
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ABSTRACT: The purpose of this paper is to study the role of wave induced radiation stress and vertical mixing in the Yellow river runoff diffusion in vertical profile. Firstly, only using a hydrodynamical model to simulate river runoff at yellow river estuary area, and then using a coupled model also to simulate yellow river runoff by introducing vertically varied radiation stress or wave induced vertical mixing. Under condition of only tide existing, river runoff diffused far away from coastal near water surface. When considering vertically varied wave radiation stress, the velocity increased and river runoff flowed near estuary not go into the sea. When considering wave induced vertical mixing, the surface velocity decreased and the value of velocity became to be uniformed. So the function of radiation stress and vertical mixing induced by wave is different. KEY WORDS: wave induced; radiation stress; vertical mixing; runoff diffusion
Wave interaction with a floating rectangular box near a vertical wall with step
type bottom topography
Joydip Bhattacharjee, C. Guedes Soares*
Centre for Marine Technology and Engineering (CENTEC), Technical University of Lisbon
Instituto Superior Técnico, Av. Rovisco Pais, 1, gal * E-mail: [email protected]
ABSTRACT: Diffraction of water waves by a floating structure near a wall with step type bottom topography is investigated under the two-dimensional small amplitude wave theory. Full solution of the problem under the potential flow approach is obtained by using the matched eigenfunction expansion method. The wave-induced forces on the structure and on the wall are studied for different water depth ratios, dimension of the structure and the distance of the wall from the structure.
Modeling of fully nonlinear wave evolution over a submerged bar
Bin-zhen Zhou 1* , Bin Teng 1, Li-fen Chen 1, De-Zhi Ning 1,2 1 State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology,
Dalian , China 2 State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering,
Nanjing Hydraulic Research Institute, Nanjing , China * E-mail: [email protected]
ABSTRACT: A three-dimensional fully nonlinear numerical wave tank (NWT) is developed by using a time-domain higher-order boundary element method (HOBEM). The source generation of waves is adopted to generate input waves. The mixed Eulerian-Lagrangian (MEL) method is utilized to track and refresh the free surface. The model is applied to three examples of wave evolution and harmonic decomposition during propogation over a submerged bar and numerical results are compared with the experimental data and the solutions of Boussinesq model. It shows that the present model agrees better with the measurements than the Boussinesq model and are more adaptable for stronger nonlinear waves. KEY WORDS: Source function; HOBEM; fully nonlinearity; wave propagation; submerged bar
Interaction of a submerged elliptic plate with waves
Wei-guang Bao 1, Kazuki Fujihashi1 ,Takeshi Kinoshita1 1 Institute of Industrial Science, University of Tokyo
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ABSTRACT: With potential applications as a breakwater, an elliptic plate horizontally submerged in waves is investigated within the scope of linear wave theory. An elliptical coordinate system is adopted, which has an advantage to represent the solution in an analytical form, i.e. an expansion of eigen functions. By means of separation of variables, it turns out that the eigen functions in the elliptical coordinates consist of the Mathieu functions and the modified Mathieu functions. The interaction of the elliptic plate with the waves is studied. The wave loads, as well as the scattered wave field, are evaluated. KEY WORDS: elliptic coordinate; Mathieu functions; eigen function expansion; Hydrodynamic forces; wave diffraction.
A shape identification problem in estimating the unknown interfacial surface for a multiple region domain
Cheng-hung Huang *, Hsi-mei Chen ** , Chia-ying Liu *
*Department of Systems and Naval Mechatronic Engineering National Cheng Kung University Tainan, China
**Department of Information Management Kung Shan University, Tainan, China
E-mail : [email protected] (C.-H. Huang). ABSTRACT: A thermal tomography problem, i.e. the shape identification problem or inverse geometry problem, in estimating the interfacial geometry for a three-dimensional multiple region domains is examined in this study based on the Conjugate Gradient Method (CGM). The accuracy of this thermal tomography analysis is examined using the simulated temperatures measured by an imaginary infrared scanner. Different temperature measurement positions and errors are considered in the numerical experiments to justify the validity of the present algorithm in solving the three-dimensional thermal tomography problem. Finally it is concluded that the reliable interfacial configurations can be estimated by the CGM. KEY WORDS: Thermal tomography problem; Interfacial geometry estimation; Conjugate Gradient Method.
A numerical study of wave propagation and run-up in water channels
2Faculty of Environmental Design, Kanazawa University, Kanazawa, Ishikawa, Japan * E-mail: [email protected]
ABSTRACT: It is important to understand how water waves propagate through water channels in order to reduce inundation damages induced by surges and/or tsunami run-up. For this purpose, a two-dimensional numerical model is developed based on Nonlinear Shallow Water Equations. In order to appropriately describe the strongly nonlinear hydrodynamics, a high-order TVD scheme is implemented. Model capabilities are confirmed through comparison with existing analytical studies including the dam-break problems, run-up and back-wash on a sloping bathymetry. The model is then applied to the study on the inundation of bore propagating in a channel of parabolic cross-section from a side breach. KEY WORDS: Bore; Inundation; Channel; Run-up; TVD scheme;
Numerical study on flow structure near two impermeable trapezoid
submerged breakwaters on slop bottoms
Yong-gang Cao 1, 2, Chang-bo Jiang 2, Yu-chuan Bai 1
（1. School of Civil Engineering, Tianjin University, Tianjin ,China; 2. School of Water Conservancy, Changsha University of Science & Technology, Changsha ,China)
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ABSTRACT: Studying on hydrodynamic characteristics in water waves propagating over two impermeable trapezoid submerged breakwaters is of great significance to research design and construction of this type of submerged breakwaters. The turbulent characteristics are discussed with cnoidal waves in the wave flume with 1:20 smooth slope.The governing equations of the vertical 2D model are the Reynolds-averaged Navier-Stokes equations. The Reynolds stress terms are closed by a nonlinear (anisotropic) k ε− turbulence transportation model. Using a VOF method for tracking the free surface and source function wave generating method.Furthermore,the supplementary discussion is made by means of numerical results. KEY WORDS: VOF method; two trapezoid submerged breakwat-ers; cnoidal waves; propagation and deformation; flow structu-re; numerical simulation
A Simulator Developed for a Twin-Pod AUV, The Marport SQX-500
Mo-qin He1*, Christopher D.Williams1,
Peter Crocker2, David Shea2, Neil Riggs2 , Ralf Bachmayer3,
1National Research Council Canada, Institute for Ocean Technology St. John's, Newfoundland, Canada, A1B 3T5
2Marport Canada Inc., St. John's, Newfoundland, Canada, A1C 6J4 3Memorial University of Newfoundland, Faculty of Engineering and Applied Science
St. John's, Newfoundland, Canada, A1B 3X5 *E-mail: [email protected]
ABSTRACT: A vertically arranged twin-pod autonomous underwater vehicle (AUV) is presently under development in St. John’s Newfoundland. A large separation of the centre of gravity (CG) and the centre of buoyancy (CB) can be achieved by placing heavy batteries and payloads in the lower pod and placing the light controller and communication electronics on the upper pod. With the large vertical separation between CG and CB the twin-pod vehicle becomes highly stable in pitch and roll and thus provides an ideal platform for obtaining photos, video and sonar images of the seabed. This paper presents the vehicle motion simulations that have been done in support of this novel AUV design and development. KEY WORDS: Underwater vehicle; simulator; modeling; hydrodynamic; manoeuvring.
Zhao-sheng Yu *, Xue-ming Shao Department of Mechanics, State Key Laboratory of Fluid Power Transmission and Control,
ABSTRACT: The Distributed-Lagrange-Multiplier based Fictitious Domain (DLM/FD) method previously proposed by Yu [J. Comput. Phys. 207 (2005), 1-27] for the simulation of fluid/flexible-body interaction problems is extended from the 2D to the 3D case in this study. We first demonstrate that the Lagrange multiplier problem can be more efficiently solved with a direct-forcing scheme instead of the original Uzawa iterations without the sacrifice of the accuracy. The type of the interpolation function (i.e. smoothed delta function) for the transfer of the quantities between the Eulerian and Lagragian frames is shown not to affect the results significantly. Secondly, the fictitious domain method is implemented in the three-dimensional case. The new 3D codes are applied to the flapping of a 3D flexible plate in a uniform flow, and the deformation of tri-leaflets at opening stage. KEY WORDS: Fictitious domain; immersed Boundary; fluid-structure interactions; flapping; leaflet
ABSTRACT: In the last years, the employment of RANS codes for a wide range of naval architecture problems is grown, since this methodology is capable of reproducing physical behaviors that are generally neglected by other models. The paper presents the results of a set of numerical tests performed employing this methodology with the aim of verifying its capability in the solution of seakeeping problem. Several condition are analyzed varying the frequency of the incident wave and its amplitude, in order to catch nonlinear effects. The results are compared with the ones achieved by a weakly nonlinear procedure based on potential theory.
KEY WORDS: RANS; BEM; Nonlinear Seakeeping.
Effects of turbulence models on numerical simulations of wave breaking and run-up on a mild slope beach
Hong Xiao 1,2, Wen-rui Huang 1,3* 1Department of Civil and Environmental Engineering, Florida State University, Tallahassee, USA
2State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University, Chengdu, China 3Tongji University, Shanghai, China
ABSTRACT: The performance of the standard k–ε model, the high-Reynolds-number k–ω model, the 1-equation k model, and the non-friction Euler model is examined against the case of wave run-up on a mild slope. A numerical model based on N-S equations and Volume Of Fluids (VOF) method is employed. Comparisons of elevation, velocity and shear stress are made among the four turbulence models against experimental data of wave run-up on a mild slope beach. It is found that before wave breaking on the slope, the outputs of the four different turbulence models agree reasonably well with each other. This suggests that during the run-up process the turbulence effect is negligible before wave breaking. Moreover, in the wave breaking zone, both the standard k–ε model and the high-Reynolds-number k–ω model predict the mean velocity field quite well, but generally under-predict the velocity and turbulent kinetic energy using wall functions on the solid slope surface. KEY WORDS: Turbulence model; shear stress; wave run-up; wave breaking;
Large eddy simulation of oscillatory boundary layer at REδ=3500
Qiang Zhang
School of Aerospace Engineering, Beijing Institute of Technology Beijing, china
E-mail: [email protected] ABSTRACT: The oscillatory boundary layer at Reynolds number of 3500 over an oscillating wall is simulated by the method of large-eddy simulation (LES). The Reynolds number is chosen as Reδ=3500 in according with one of the well-known experimental cases (Test No. 10, Ref. [3]). The simulation presents the first- and second-order statistics of the oscillatory boundary layers, which are in good agreement with the experimental data. By investigating of the existence of the logarithmic layer in the velocity profiles, the fully developed turbulence state is identified; During half a cycle (90°-270°), the logarithmic layer starts to appear at about 110°, and lasts till 250° in the current simulation. The evolutions of the turbulent energy spectra are also illustrated. KEY WORDS: Oscillatory boundary layer; LES; turbulent; spectra; coherent structure.
ABSTRACT: In the present study, a hybrid RANS-LES (Reynolds Averaged Navier-Stokes equation – Large Eddy Simulation) model is developed for the simulation of open-channel T-junction flows. The hybrid approach can save computational effort comparing to the LES approach. The comparison between the computational results and the detailed experimental data shows that this relatively new modeling approach is more accurate than the RANS approach in the prediction of the combining flows in T-junctions. KEY WORDS: Hybrid RANS-LES model, open-channel flow, T-junction, turbulence modeling.
Study of droplet deformation, heat-conduction and solidification using incompressible smoothed particle hydrodynamics method
Hong-bing Xiong, Jian Zhu
Department of Mechanics, Zhejiang University, Hangzhou, China
ABSTRACT: This paper presents a numerical model based on incompressible smoothed particle hydrodynamics (SPH) method to simulate the deformation, heat-conduction and solidification process of a droplet impinging on a substrate. Continuum, momentum and energy equations of the fluid flow are solved using SPH method, with van der Waals force accounting for the surface tension and Fourier's law for heat conduction. Incompressible smoothed particle hydrodynamics method (ISPH) is used here instead of weakly compressible smoothed particle hydrodynamics method (WSPH), to satisfy the fluid incompressibility. Effects of rough and smooth substrates are also taken into account. Results show that the droplet begins to deform and spread, followed by solidification. Also, the temperature of droplet falls faster in the rough one, and this may attribute to the roughness. KEY WORDS: ISPH; deformation; heat-conduction; solidification.
Three-dimensional numerical simulation of flow around a circular cylinder
under combined steady and oscillatory flow
Ming Zhao *, Liang Cheng , Hong-wei An
School of Civil and Resource Engineering, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia
* E-mail: [email protected] ABSTRACT: Combined steady and oscillatory flow past a circular cylinder is investigated numerically by three-dimensional Direct Numerical Simulation (DNS). The incompressible Navier-Stokes equations are solved by finite element method (FEM). The aim of this study is to investigate influence of the existence of steady current on the flow regime and hydrodynamics forces. The computational results of pure oscillatory flow past a circular cylinder agree well with the experimental data. The flow ratios (ratio of current velocity to oscillatory velocity amplitude) are 0.0, 0.2 0.5 and 1.0 in the study. The influence of the flow ratio on the vortex shedding regime and hydrodynamic forces on the cylinder are investigated numerically. KEY WORDS: Circular cylinder, steady flow, oscillatory flow, hydrodynamic forces, vortex shedding
ABSTRACT: In the context of fluid mixing in microelectromechanical systems, Lagrangian mass transport induced by peristaltic waves traveling on the boundaries of a two-dimensional rectangular closed channel is studied analytically. Based on the Lagrangian description, an asymptotic analysis is performed to generate explicit expressions for the leading-order oscillatory as well as the higher-order time-mean mass transport velocities as functions of the wave properties. For small steady-streaming Reynolds number, we have revisited the problem studied previously in the literature, but with all the results fully presented in the Lagrangian sense. KEY WORDS: Peristaltic pumping; steady Lagrangian drift; microchannel flow.
Studies on the oscillation behavior of a flexible plate in the wake of a D-cylinder
Ding-yi Pan 1, Hua Liu2, Xue-ming Shao 1* 1Department of Mechanics, State Key Laboratory of Fluid Power Transmission and Control,
Zhejiang University, Hangzhou, China 2China Ship Research and Development Academy, Beijing, China
ABSTRACT: This paper studies the oscillation behavior of a flexible plate in the wake of a D-section cylinder. The interaction between the flexible body and its surrounding vortices is investigated. A modified immersed boundary method is used to solve the motion of fluid, integrated with a linearized Euler-Bernoulli beam model to govern the motion of the flexible plate. Results show that, when the distance between cylinder and plate is small, the surface of the plate is surrounded by vortices layers and the plate oscillates periodically, with amplitude similar to the cylinder movement. However, if the distance becomes large, we find that the vortices are shed from the D-cylinder in front of the plate, and the incoming vortices make the plate oscillate with large amplitude at the beginning and then slant laterally. Also, the amplitude becomes smaller compared to the case of the small distance. KEY WORDS: oscillation; vortex wakes; flexible body; fluid-structure interactions (FSI)
An integrated model of wave-seabed-structure interactions
Ji-sheng Zhang 1, Bo Wang 1, Dong-sheng Jeng 1*, Philip L. –F. Liu 2, Ping Dong 1 1Division of Civil Engineering, University of Dundee, Dundee DD1 4HN, UK
2School of Civil and Environmental Engineering, Cornell University, New York , USA * E-mail: [email protected]
ABSTRACT: The phenomenon of wave-seabed-structure interactions have occurred in the marine environment with a coastal permeable (or partially permeable) structure, which has attracted great attention from coastal engineers involved in the design of marine structures. In this study, a porous seabed model based on Biot’s consolidation equation and pore-elastic theory is integrated into the COBRAS wave-structure model. This integrated model is verified by the laboratory experiments. Some dominant factors affecting the wave motion and its induced seabed response are examined by using this model, including wave parameters and structure properties. KEY WORDS: Wave motion; Porous seabed; Submerged permeable breakwater; Mathematical model
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Numerical simulation and comparison of potential flow
and viscous fluid models in near trapping of narrow gaps
Lin Lu 1*, Liang Cheng 2, Bin Teng 3, Liang Sun 4
1 Center for Deepwater Engineering, Dalian University of Technology, Dalian,China 2 School of Civil and Resource Engineering, The University of Western Australia, Crawly, Australia
3 State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian,China 4 Centre for Offshore Research and Engineering, Department of Civil Engineering, National University of
ABSTRACT: Numerical simulation results of fluid oscillation in narrow gaps subjected to incident water waves are presented in this paper. Both viscous fluid model and potential flow model with artificial viscous damping are employed to investigate wave motions in a single narrow gap separated by twin bodies and double narrow gaps formed by three identical bodies. Variation of wave heights in the narrow gaps with incident wave frequency is compared with experimental data available in literatures. The numerical results demonstrate that both the viscous fluid model and the potential flow model are able to predict the resonant frequency reasonably well. However the conventional potential flow model (without introducing the artificial viscous damping) significantly over-predicts the wave height in narrow gaps around the resonant frequency. The potential flow model with artificial damping predicts resonant wave heights well with a properly tuned (or calibrated) damping coefficient. The horizontal wave force on the individual body is also examined in this work. It is found that a properly calibrated damping coefficient is also very important for estimating the horizontal wave forces on the structures. A damping coefficient of 0.4 in the potential flow model is found to result in satisfactory predictions of wave heights in the narrow gaps and the horizontal hydrodynamic force for the cases considered in this work. KEY WORDS: Near Trapping; Fluid Resonance; Narrow Gap; Potential Flow Model; Viscous Fluid Model; Boundary Element Method; Finite Element Method
Large transient waves generated through modulational instability in deep water
2Professor, Department of Hydraulic and Ocean Engineering, NCKU Tainan, China
ABSTRACT: The long-term evolution of nonlinear wave train in deep water with varied initial wave steepness is investigated experimentally in a super wave flume (300 m long, 5 m wide, 5.2 m deep). The initial wave train is the combination of one carrier wave and a pair of imposed sideband components. Increasing modulation of wave train is observed due to sideband instability until a critical value which either initiates wave breaking or reaches the maximum modulation. The observed maximum local wave steepness increases rapidly with the increase of the initial wave steepness, and levels off at initial wave steepness roughly equal to 0.15 despites that the data exhibits a little scattering. The normalized crest elevation at peak modulation increases rapidly with initial wave steepness and approached a maximum value almost equal to 3.5 which corresponds to initial wave steepness around 0.15c ck a = . The results reveal that the large transient wave such as freak wave could be generated during the propagation of nonlinear wave trains in deep water through sideband instability. KEY WORDS: sideband; modulation; transient wave; breaking.
ABSTRACT: This study investigates the flow field induced by the tilting lift of a large object from a rigid porous seabed and the induced force acting on the object using an analytical approach. In the corners between the object and the seabed, we assume the flow is a corner flow with a low Reynolds number, and the porous media flow in the seabed obeys Brinkman equations. The complete boundary conditions for viscous flow, including the continuity of velocities and stresses, are utilized at the seabed-water interface. The Helmholtz decomposition theorem, which decomposes the flow field into irrotational and rotational parts, and a perturbation expansion are employed to solve the boundary-value problem. Leading-order analytical solutions for the flow in the water and in the porous seabed are presented, indicating that the flow inside the corners is not a parallel flow, and the porous media flow inside the seabed is a Stokes boundary layer flow that does not obey Darcy’s law. KEY WORDS: Lifting of object; breakout phenomenon; porous media flow; boundary layer; low-Reynolds-number flow.
Coupling of CFD model and FVCOM to predict small-scale coastal flows
Xiu-guang Wu 1,2, Han-song Tang 2,*
1Zhejiang Inst. of Hydraulics & Estuary, Hangzhou, China 2Dept. of Civil Eng., City College, City Univ. of New York, New York, NY 10031, USA
ABSTRACT : In order to accurately simulate small-scale coastal ocean phenomena, we propose to couple a computational fluid dynamics (CFD) model with the Unstructured Grid Finite Volume Coastal Ocean Model (FVCOM). The CFD model resolves small-scale flows, the FVCOM predicts large-scale background currents, and the resulting hybrid system is able to capture flow phenomena with spatial scales from centimeters to hundreds of kilometers. The coupling is two-way and realized using domain decomposition with aid of Chimera overset grids. Numerical examples are presented to demonstrate the feasibility and performance of the proposed hybrid approach. KEY WORDS: Multi-scale; Coastal ocean flow; CFD; FVCOM; Chimera overset grids.
Research on particle size distribution in rectangular turbulent channel flow
Fu-jun Gan 1, Jian-zhong Lin 1, 2* 1 State Key Laboratory of Fluid Power Transmission and Control, Zhejiang University
2 College of Metrology and Measurement Engineering, China Jiliang University Hangzhou, China
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ABSTRACT: Large eddy simulations of three-dimensional particle-laden turbulent channel flow are performed for Re = 13800. The flow results are validated using the experimental data and good agreements are achieved. TEMOM is employed to deal with PGDE, which describes PSD, involving the effect of shear-induced coagulation, which is greatly affected by the effects of turbulent transport and preferential concentration, represented by radial relative velocity and radial distribution function, respectively. Particles with four different stokes number are considered to study the above effects on the evolution of PSD. In the results, the distributions of particle number concentration, polydispersity, particle diameter are detailed discussed. KEY WORDS: turbulent channel flow; large eddy simulation; Taylor-series expansion moment method; relative velocity; preferential concentration.
Numerical simulations of viscous flows around surface ship
by level set method
De-cheng Wan * , Zhi-rong Shen, Juan Ma
State Key Laboratory of Ocean Engineering, School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, China
ABSTRACT: Numerical simulations of viscous flows around surface ships by coupling the 3D incompressible RANS equations with level set method are presented in this paper. The finite difference method is used to discretize the RANS equations with turbulent model SST ω−k . The fully nonlinear boundary condition at the free surface is satisfied at each time step and the evolution of the free surface is achieved by using the level set method. The coupled solver is applied to a benchmark case of viscous flows around an advancing Wigley ship with various Froude numbers. The computational results are in excellent agreement with experimental data. The simulations reveal clearly the generation and evolution of bow and stern waves. KEY WORDS: Level set method; RANS equations; ship flows; viscous wave making.
Investigation on forces exerted on a sediment particle in current and wave boundary layer through 3D lattice Boltzmann simulation
Qing-hi Zhang *, Lei Ding
School of Civil Engineering, Tianjin University & Key Laboratory of Harbor and Ocean Engineering (Tianjin University), Ministry of Education,Tianjin , China
ABSTRACT: The 3-D lattice Boltzmann method is applied to evaluate the forces exerted on a stationary spherical particle in current and wave boundary layer flow in order to analyze the forces contributing to the incipient motion of the sediment particle. Results indicate that for current, the forces reach statistically steady finally at a relative low particle Reynolds number (less than 40). The streamwise drag force is the main driven force while the effect of the spanwise force can be ignored. The reason that results in the phenomenon is also discussed. As for the wave, the cyclical nature of the flow makes the evolution of drag and lift forces become quasi-periodic. The streamwise drag force is still the main driven force, but it changes direction with the flow. Meanwhile, the spanwise vorticity and the pressure around the particle show asymmetric distribution. The influence of spanwise force on the particle can not be neglected. KEY WORDS: lattice Boltzmann method; drag force; lift force; a stationary spherical particle; smooth turbulent open-channel flow; oscillatory boundary layer flow
Three dimensional numerical simulation of bore type tsunami propagation and run up on to a dike
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Indradi Wijatmiko1, Keisuke Murakami2 1Interdisciplinary Graduate School of Agriculture and Engineering, University of Miyazaki, Miyazaki, Japan
1-1 Gakuen Kibanadai Nishi, Miyazaki, Japan E-mail: [email protected]
2Department of Civil and Environmental Engineering, University of Miyazaki, Miyazaki, Japan 1-1 Gakuen Kibanadai Nishi, Miyazaki, Japan
E-mail: [email protected] ABSTRACT: Tsunami increases its height on the shallow water area and may transfers into bore when it breaks. Bore type tsunami sometimes produces huge forces and causes large damages on coastal infrastructures. In order to mitigate tsunami damages, bore type tsunami propagation, run-up and its characteristics need to be understood. And aside of experimental study, numerical simulation provides principal physical quantities with higher resolution in time and space. This study discus the validity of a numerical simulation based on VOF method, CADMAS-SURF, and characteristics of bore propagation on to a dike. KEY WORDS: Bore type Tsunami; Tsunami inundation; VOF method; CADMAS-SURF; Wave force.
3-D numerical simulations of violent sloshing by CIP-based method
Chang-hong Hu 1*, Kyung-Kyu Yang 2, Yong-hwan Kim 2 1 Research Institute for Applied Mechanics, Kyushu University, Japan
2 Department of Naval Architecture & Ocean Engineering, Seoul National University, Korea * E-mail: [email protected]
ABSTRACT: The violent sloshing flow inside a rectangular tank is computed by the CIP (Constrained Interpolation Profile) [1] based Cartesian grid method. Two kinds of CIP scheme, the original CIP scheme and the RCIP scheme, have been applied to the flow solver. 2-D and 3-D computations using the two CIP schemes are carried out and their performances are discussed by comparing the results of the impact pressures on the wall and the free surface profiles to the experimental measurements. KEY WORDS: violent sloshing, three-dimensional simulation, CIP, RCIP
Forces due to exterior singularities upon 2- and 3-dimensional bodies
Seung-joon Lee Department of Naval Arch. & Ocean Eng., Engineering College, Chungnam National University
ABSTRACT: Thrust deduction, or the resistance increase, is not fully investigated probably because of the complexity of the flow pattern in the stern region. In this work, it is assumed that the theory of potential flows may represent the most significant portion of the physics of the phenomena. Hence the propulsor and other devices in the stern region are represented by exterior singularities and their effects upon the resistance increase are estimated by taking a circular cylinder and a sphere as the 2- and 3-dimensional body, respectively. Results for a circular cylinder are summarized, and those for a sphere are given more attention. KEY WORDS: thrust deduction; potential flows; singularities; circular cylinder; sphere.
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Numerical simulation of cavity flow induced noise by LES and FW-H acoustic analogy
Nan Zhang *, Hong-cui Shen, Hui-zhi Yao
China Ship Scientific Research Center, Wuxi, China * E-mail: [email protected]
ABSTRACT: The predictions of cavity flow and flow-induced noise are two important and complex issues in fluid-acoustic coupling field. Numerical studies for these issues are performed in the paper by large eddy simulation (LES) and FW-H acoustic analogy. Firstly, the wall pressure fluctuations of plate, foil, shutter hole are computed and compared with experimental results. The robustness of large eddy simulation in unsteady flow calculation is analyzed. Secondly, the calculation of a 2-D cavity flow are accomplished. The power spectrum of pressure fluctuations is compared with measured data and the vorticity distribution is analyzed. Finally, the flow induced noises of two 3D cavities are predicted. The computed results are compared with experimental data of Large Circulation Channel in CSSRC. It shows that the numerical prediction method in the paper is credible. KEY WORDS: cavity flow; flow induced noise; wall pressure fluctuations; Large eddy simulation; FW-H equation
Numerical investigation of a swirling flow under the optimal perturbation
Cheng Chen 1 , De-jun Sun 1* 1Department of Modern mechanics, University of Science and Technology of China
Hefei , China * E-mail: dsun@ ustc.edu.cn
ABSTRACT: The nonlinear evolution of 3-D instability of a viscous swirling flow, namely, the Oseen vortex, is addressed by direct numerical simulation with a Reynolds number equal to 5000. The global optimal perturbation is considered as the initial perturbation. In axisymmetric cases, three flow regimes are found: (1) the linear growth; (2) the decay of perturbation energy; (3) secondary energy growth. The linear energy growth, which is characterized by the amplification of radial perturbations, is arrested by the interaction between the vortex ring and the Oseen vortex core. The development of the vortex structure is also investigated for non-symmetric flows. KEY WORDS: Oseen vortex; optimal perturbation; transient growth; nonlinear evolution.
SPH simulation of green water and ship flooding scenarios
D. Le Touzé1*, A. Marsh1, G. Oger2, P.-M. Guilcher2, C. Khaddaj-Mallat1, B. Alessandrini1, P. Ferrant1
1Fluid Mechanics Lab., Ecole Centrale Nantes / CNRS, Nantes, France 2HydrOcean, Nantes, France
ABSTRACT: Flooding of a ship's deck (greenwater) or within its internal compartments can severely restrict the operational ability of the vessel, and the safety of its cargo. In severe circumstances such as those produced by freak waves or hull damage, the vessel can become unstable causing it to sink and/or capsize. The flows produced by such events tend to be highly dynamic, with large amounts of free surface deformation. For this reason, SPH is a valuable method for predicting the physics of such flows. In this paper, SPH is used to predict fluid behaviour for two different flooding scenarios. The first is the interaction between a vessel (represented by a rigid body) and undulating travelling waves. The predicted water heights on the deck are compared to experimental results in [1]. The second is the transient flooding behaviour that occurs during, and immediately after a side collision between two vessels. Water heights are measured close to the point of impact within the vessel. The measurements are compared to experimental results in [2].
ABSTRACT: This contribution presents our recent progress on developing an efficient fully-nonlinear potential flow model for simulating 3D wave-wave and wave-structure interaction over arbitrary depths (i.e. in coastal and offshore environment). The model is based on a high-order finite difference scheme OceanWave3D presented in [1, 2]. A nonlinear decomposition of the solution into incident and scattered fields is used to increase the efficiency of the wave-structure interaction problem resolution. Application of the method to the diffraction of nonlinear waves around a fixed, bottom mounted circular cylinder are presented and compared to the fully nonlinear potential code XWAVE as well as to experiments. KEY WORDS: High-Order Finite Differences ; Nonlinear Decomposition ; Scattering ; OceanWave3D ; XWAVE
High effective WENO scheme for transonic inviscid flow computation on a helicopter rotor in hover
Li Xu 1,2, Pei-fen Weng 2*, Ai-ming Yang 3, Jue Ding 2 1Department of Mathematics and Physics, Shanghai University of Electric Power
Shanghai, China 2Shanghai Institute of Applied Mathematics and Mechanics, Shanghai University
Shanghai, China 3Department of Mechanics and Engineering Science, Fudan University
ABSTRACT: A high-order upwind scheme with high efficiency has been developed to compute the inviscid flow of a helicopter rotor in hover. For rotary-wing wake capturing, an improved fifth-order weighted essentially non-oscillatory (WENO) scheme is adopted to interpolate higher order left and right states across a cell interface with Roe Riemann solver updating inviscid flux. To improve the efficiency and convergence to steady state, three-level V-cycle multigrid relaxation scheme is used. The performance of the schemes is investigated in a transonic inviscid flow around hovering rotor. The results reveal that WENO has the great capabilities to capture shock with high resolution and has a lower numerical dissipation than MUSCL for capturing wake vorticity. Moreover, multigrid scheme can accelerate convergence to a great extent.
Numerical study of high-order Lagrangian structure functions in a turbulent channel flow with low Reynolds number
Jian-ping Luo 1,3, Zhi-ming Lu 2*, TatsLo Ushijima3, Osami Kitoh3, Xiang Qiu 1, Yu-lu Liu 1,2 1Shanghai Institute of Technology, Shanghai, China
2Shanghai Institute of Applied Mathematics and Mechanics, Shanghai University, Shanghai, China 3Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan
ABSTRACT: The scaling exponents of Lagrangian velocity structure functions from orders 1 to 10 in a low Reynolds number turbulent channel flow are investigated by using direct numerical simulation. The Reynolds number Reτ is 80 (based on friction velocity on the wall). The Lagrangian velocity structure functions are shown to obey the scaling relations <Δvq(τ)>~τζL(q). The scaling exponents are normalized by ζL(2) (so-called ESS procedure). The coincidence between the theoretical predictions and numerical calculations is very good for the longitudinal scaling exponent in the channel center. It is also found that the high-order longitudinal scaling exponents agree with theoretical values better than those for the transverse direction. KEY WORDS: Intermittency; Lagrangian Scaling Exponents; Turbulent Channel Flow
Free-surface flow past a submerged cylinder
Meng-yu Lin 1* , Liang-hsiung Huang 1 1 Department of Civil Engineering, National Taiwan University
ABSTRACT: This study employs a Lagrangian frame numerical method to investigate two-dimensional free-surface flow induced by a submerged moving cylinder. This method combines the advantages of vortex methods and boundary integral methods, and is capable of capturing the complex motion of free surface and vortices. A series of computations are performed to investigate the effects of Froude number, the depth of submergence and still water depth on the flow motion. Free surface deformation, wake vortex and hydrodynamic forces are studied. KEY WORDS: Free surface flow; submerged cylinder; vortex; vortex methods; boundary integral methods.
IBM/ICM method for interactions between moving bodies and free surfaces
Deng Jian *, Xie Fang-fang, Shao Xue-ming, Yu Zhao-sheng School of Aeronautics and Astronautics, Zhejiang University, Hangzhou, China
*Email: [email protected] ABSTRACT: The IBM/ICM method is developed to simulate the interactions between moving bodies and free surfaces. This method is a combination of Immersed Boundary Method (IBM) and Interface Capture Method (ICM), inheriting the IBM’s capability of using non-body conformal grids to represent the effect of a moving body in the flow by only adding a pseudo body-force in the right side of Navier-Stokes equations, as well as the capability of ICM, i.e. VOF, to capture the interface between two immiscible fluids. In the current paper, the Lagrange-multiplier based IBM method is employed and the volume of fraction (VOF) is introduced as an indicator function to mark the different fluids. The numerical method is validated by the case of high-speed impact by a horizontal circular cylinder, which exhibits a wide range of dynamical response characteristics, i.e. the formation of a cavity and
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induced pressure waves in the late stages of the cavity collapse, depending primarily on the projectile’s impact velocity. KEY WORDS: Immersed Boundary Method; Interface Capture Method; IBM/ICM Method.
An experimental study of compressed air generation using a pendulum wave energy converter
2School of Environmental Design, Kanazawa University, Kanazawa, Ishikawa, Japan *Email: [email protected]
ABSTRACT: This study describes a novel system of compressed air generation using a pendulum wave energy converter installed in a coastal defense structure. The objective of this study is to understand how much energy from the incoming waves can be captured for use by the system. Laboratory experiments were carried out to determine the effects of wave and system load conditions on energy conversion efficiency and wave reflection. The test results show that the system can operate with a high degree of efficiency under standing wave and high-load conditions. A reduction of wave reflection can be achieved by the system under a wide range of wave conditions. KEY WORDS: Wave energy; wave reflection; pendulum motion; compressed air; renewable energy.
An experimental study on leakage flow in different geometrical disk seals
Wei Zhao 1*, Torbjørn K. Nielsen1,Jan Tore Billdal2 1Norwegian University of Science and Technology, Trondheim, Norway
ABSTRACT: This paper presents an experimental study on the leakage flow in rotor-stator system. The experimental set-up of the rotor-stator system is a simplification of a Francis turbine runner with focus on the seals. It consists of a motor, a bearing, a shaft, a fixed rotor made of steel, a pump and a plastic ring fixed on the steel rotor, which can be replaced with different geometrical pads to test various seals. A small radial clearance (0.2mm) between the rotational disk and stator is settled. Leakage loss, pressure variation under the rotational disk and pressure difference between above and below the disk for various geometrical seals is measured at different rotational speeds. The results indicate that the rotational disk can reduce the leakage loss as the speed increases and the performance of disk without pads is better than the disk with straight pads under the same supply flow. KEY WORDS: Seals; leakage loss; disk friction; experiment; Francis turbine.
Well test analysis of viscoelastic polymer solution
Wei-li Yang, Hong-jun Yin, Hui-ying Zhong, Si-yuan Meng Key Laboratory of Enhanced Oil and Gas Recovery (Daqing Petroleum Institute),
ABSTRACT: With the consideration that the polymer solution has the characteristics of viscosity and elasticity, the seepage flow model is established. The model is solved by the finite difference method. Then the type curves are drawn. The influences of the skin factor, the wellbore storage factor, the consistency coefficient, the power law index and the elasticity sensitivity factor of the polymer solution on the type curves are analyzed. This study shows that it is very necessary to consider the elasticity in the well test analysis of viscoelastic polymer solution. KEY WORDS: viscoelasticity; seepage flow model; polymer solution; well test; pressure.
ABSTRACT: Wing-In-Ground Effect (WIG) Craft (Russian ekranoplans) offers a new transport solution somewhere between boat and aircraft and may revolutionize the future fast sea transportation in terms of its characteristics. Aerodynamic characteristics of WIG craft near curved ground are investigated. Computational fluids dynamics (CFD) method is applied into the study due to limitation of wind tunnel test in simulating curved ground. Numerical techniques including sliding meshing and dynamic meshing are established and compared in the study to analyze effect of curved ground on WIG craft. Aerodynamics and flow features of WIG craft with and without course angles in cruise are taken into consideration in the current work. The study will hopefully clarify the understanding of the aerodynamics of WIG craft. KEY WORDS: WIG craft; curved ground; computational fluid dynamics; course angle.
The profile-linear average velocity for the transition in pipes based on the method of LES*
Yong-hui Liu, Guang-sheng Du, Zheng-gang Liu, li Li, Li-li Tao
School of energy and power engineering, Shandong University, Jinan, China E-mail: [email protected]
ABSTRACT : The ultrasonic flowmeter has been widely used in the industrial flow measurement. The flow measurement accuracy depends on the relationship of the profile-linear average velocity. But this relationship of the transition zone is not available at present. In this paper, the characteristics of transition flow with specific Re number in pipes are researched. The ε−k model and LES(Large Eddy Simulation) model are respectively used to calculate the flow field of the transition zone, and the experiment results show that the LES model is more effective than the ε−k model. The relationship of the profile-linear average velocity for the transition zone in pipes is obtained by the calculated results of the LES model and it is proved that there is a big error using the tradition relationship based on the turbulence flow to calculate the profile-linear average velocity relationship of the transition flow. The research results of this paper can improve the measurement accuracy of ultrasonic flowmeters and provide theoretical basis for the research on the whole transition flow. KEY WORDS: Ultrasonic flowmeter; LES model; profile average velocity; linear average velocity; pipe.
An integrated design system for turbomachinery
Xu-wen Qiu, Mark Anderson, David Japikse
Concepts NREC, 217 Billings Farm Road, White River Junction, VT 05001-9486, USA E-mail: [email protected]
* Project supported by the National Science Foundation of China(Grant No. 10972123)
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ABSTRACT: This paper outlines an integrated design system for turbomachinery, particularly machines such as gas turbines, hydraulic turbines, pumps, and propellers commonly found in marine operations. The system incorporates flow modeling, structural analysis, and manufacturing simulation under one integrated design environment, which allows effective sharing and transfer of information among different stages and disciplines of the design, thus optimizing the design process. The design starts with 1D meanline modeling, which allows designers to explore a vast design space and produces a basic flow path and preliminary performance prediction. From the meanline results, an initial 3D geometry model can be constructed. This geometry model serves as the core of the design system on which further aerodynamic and mechanical optimization, such as full 3D computational fluid dynamics (CFD) analysis and finite element analysis (FEA), can be subsequently performed. Furthermore, a computer-aided manufacturing (CAM) component is also part of the design system. The early inclusion of 5-axis manufacturing considerations in the design process can help reduce overall costs while avoiding the expensive overhaul of the aerodynamic and structural design late in the process. This integrated approach ensures that the final design not only meets the performance target, but also satisfies the requirements of structural integrity and manufacturability. KEY WORDS: Turbomachinery; Design Optimization; Computer Aided Engineering (CAE); Finite Element Analysis (FEA); Computer Aided Manufacturing (CAM).
Experimental study on a dynamic contaminant release into overlying water-body across sediment-water interface
Jing-yu Fan, Dao-zeng Wang *, Kun Zhang
Shanghai Institute of Applied Mathematics and Mechanics, Shanghai University, Shanghai 200072, China * E-mail: [email protected]
ABSTRACT: The dynamic release process from the contaminated sediments into the overlying water-body was experimentally investigated in an open channel flume under different hydrodynamic conditions. The time-dependent concentration variation and relative significance of the static release due to diffusive transport and the dynamic release due to resuspension/settling of the sediments were determined based on the obtained data. The experimental results indicate that before reaching an equilibrium stage, the dynamic release caused by the resuspension/settling of the sediments is much more effective than the static release by the molecular diffusion in an initial release stage. The impacts of the static and dynamic release on the overlying water column are further analyzed under different flow velocity and water depth conditions. KEY WORDS: Sediment-water interface; contaminant; dynamic release; overlying water-body; sediment resuspension.
PIV studies on turbulence structure in air/water interface with wind-induced water waves
Michio Sanjou 1, Iehisa Nezu1 , Akihiro Toda 1 1Department of Civil Engineering, Kyoto University, Katsura Campus, Kyoto
ABSTRACT: When wind appears over the free surface, water waves and turbulence are generated by an interfacial shear stress. In particular, turbulent diffusion promotes significantly mass and momentum transport beneath the interface between the water and air significantly in ocean and lakes, and thus it is very important for global environment problems to reveal such turbulence property and coherent structure. Simultaneous measurements of velocities and free-surface elevation allow us to conduct reasonably the phase analysis of the coherent structure in interfacial shear layer. Furthermore, multi-point measurements such as PIV are very powerful to detect the space-time structure of coherent motions. Therefore, in the present study, we developed a specially designed PIV system which can measure the velocity components and surface-elevation fluctuation simultaneously by using two sets of high-speed
ABSTRACT: The braking force produced by tugboat has been scarcely examined and little data on the proper characteristics of the braking force can be obtained. Therefore, it is necessary to investigate the braking performance of tugboat. In this paper, the braking force characteristics of tugboat-self in braking condition are obtained and the related unstable phenomena is pointed out and analyzed according to the results of model experiments. Furthermore some new understanding on the braking co-operation by using tugboat is suggested. KEY WORDS: Tugboat, Braking Force, Braking Force Characteristics, Braking Methods, Unstable Motions
Experimental investigation of drag reduction in micro-channels with surfaces
adsorbed hydrophobic nanoparticles
Qin-feng Di 1*, Chun-yuan Gu 1, Xin-liang Wang 1 , Ren-liang Zhang 1, Wei-peng Ding 1 1Shanghai Institute of Applied Mathematics and Mechanics, Shanghai University,
ABSTRACT: Reconstructing the capillaries and complicated core micro-channels by using the adsorption method with Hydrophobic Nanoparticles(HNPs) can change the properties of walls of micro-tubes and hence decrease the water resistance. It is shown that under the conditions of pressure this can increase obviously the water flux in micro-tubes or micro-channels. It is further found that the adsorption method with HNPs can increase dramatically the water phase permeability of core and decrease the water resistance. This is because the HNPs of SiO2 can enhance the hydrophobility of micro-tube walls, which would generate the water-flow-slip effects. This method is of great significance to reduce the resistance in core’s micro-channels with complicated structures, and is expected to be a new technology to decrease the water injection pressure of reservoir. KEY WORDS: Micro-channels, capillary; hydrophobic nanoparticles SiO2; slip effect; drag reduction.
Development of an acoustic instrument for bubble size distribution measurement
Xiong-jun Wu 1* , Georges L. Chahine1 1DYNAFLOW, INC. ,Jessup, Maryland, U.S.A
∗ Supported by “the Fundamental Research Funds for the Central Universities”, 017008.
ABSTRACT: Measurement of bubble size distribution and void fraction is of vital importance in many multi-phase flow applications. This paper describes an acoustics based device, the ABS Acoustic Bubble Spectrometer®, which can conduct measurements accurately in near real-time in a cost-effective fashion. By propagating short bursts of sound at different frequencies through bubbly medium, it measures frequency dependent attenuations and phase velocities of the acoustic waves and uses them to obtain the bubble size distribution (number of bubbles per size) by solving an inverse problem. Recent developments, both in hardware and software, as well as their validations are presented, these new advancements enable the ABS to measure void fractions up to 3x10-3 with bubble sizes ranging from 10 μm to 3mm. KEY WORDS: bubble size distribution; void fraction; acoustic; multi-phase flow.
Numerical and experimental investigations of the
unsteady cavitating flow in a vortex pump
Alexander Steinmann1, Hendrik Wurm2, Alfred Otto3
1,2 Group Research and Technology Center – Fluid Mechanics, WILO SE Nortkirchenstr. Germany
ABSTRACT: In order to develop an understanding of the flow conditions in Vortex Pumps, numerical investigations (commercial URANSE-CFD-Solver ANSYS CFX, Volume-of-Fluid Rayleigh-Plesset cavitation model, eight impeller revolutions) and experimental investigations (High-Speed Exposures of the cavitation clouds through acrylic glass window) have been carried out. A further objective was to investigate the URANSE-CFD method using the mentioned cavitation model regarding numerical stability and accuracy. KEY WORDS: vortex pump, centrifugal pump, sewage water pump, cavitation, CFD, URANSE
An experimental study of inertia and drag coefficients for a truncated circular cylinder in regular waves
Zhi-da Yuan, Zhen-hua Huang * 1 School of Civil and Environmental Engineering, Nanyang Technological University,
ABSTRACT: It is of academic and practical importance to predict accurate wave loads on cylindrical members of finite length. In this study, the in-line force on a small segment of a vertical circular cylinder of various truncated lengths was experimentally investigated in regular waves. Based on Morison equation, the inertia and drag coefficients (CD and CM) were evaluated and presented as a function of KC number for various values of relative truncated length in order to understand 3-D end wake effects on the truncated cylinder. The factors that may affect the determination of CD and CM were also discussed. A weighted least square method was employed to improve the predictive accuracy of maximum measured forces.
ABSTRACT: Silt screen is a type of flexible barrier that has been widely deployed for the purpose of sediment containment in an aquatic environment. Yet, its working mechanism is still largely unknown. In this study, the authors presented the findings of an investigation of the hydraulic performance of silt screen using Particles Imaging Velocimetry (PIV) technique. The experiments were conducted in a 30 cm-wide flume, with a silt screen spanned across the whole width, normal to the flow. Three average flow velocities, U0 of 0.5 m/s, 0.1 m/s, and 0.2 m/s and different values of the penetration ratio (the ration between screen’s penetration depth and flow depth) were simulated in the experiments. PIV images of the flow approaching the screen and that at the lee side of the silt screen were captured in the vertical mid-plane of the flume. The images were then processed, and analyzed to determine the velocity distribution, turbulence characteristics and streamlines patterns of the flow in the vicinity of the silt screen. Preliminary results showed that underflow through the gap between silt screen’s lower end and the flume’s bottom could be large. The experimental results also suggested a distinct change of flow patterns with the formation of recirculation areas at both sides of the screen. This paper attempts to elucidate the hydraulic performance of silt-screen in response to the magnitude of the environmental flow and different scenarios of screen configurations.
KEY WORDS: silt screen; Particles Imaging Velocimetry; recirculation; flow diversion; sediment containment, silt screen deformation. Water tunnel experimental investigation on the drag reduction characteristics of
the traveling wavy wall
Yan Yao 1, 2*, Jin-ling Luo 2, Chuan-jing Lu 1, 3, Hong-yu Mao 2
1. Department of Engineering Mechanics, Shanghai Jiaotong University, Shanghai, China. 2. Beijing Electromechanic Engineering Institute, Beijing, China. 3. State Key Laboratory of Ocean Engineering Shanghai, China.
ABSTRACT: Drag reduction experiment of the traveling wavy wall at high Reynolds number is conducted. A suit of traveling wavy wall device is developed. The drag forces of the traveling wavy wall with various wave speeds (c) are measured under different water speeds (U) in the K15 cavitation water tunnel and are compared with that of the flat plate. The results show that the mean drag force of the traveling wavy wall have decreased and then increased with oscillation frequency increasing at the same flow speed. Under different flow speeds, when traveling wave wall reached to the minimum of drag force, the corresponding the ratio of the wall motion phase speed c to flow speed U, c/U is slightly different. Within the parameters of the experiment, when c/U reaches a certain value, the drag force of the traveling wavy wall can be less than that of the flat plate. The drag reduction can be up to 42%. Furthermore, as the value of c/U increases, the traveling wavy wall can restrain the separation and improve the quality of flow field. KEY WORDS: flow control; drag reduction; traveling wavy wall; water tunnel test
ABSTRACT: In this study, a jump matching correlation scheme is proposed. For the multi-grid, iterative particle image distortion analysis, the coarse grid solutions are not obtained from coarse pixel image constructed by binning small pixels to large pixel, but by jumping the interrogation window the number of pixels specified during the particle image matching process. With the jump matching scheme applied and particle image interpolated, the central difference particle image pattern matching and image distortion analysis are easily linked together to resolve flow fields from coarsest grid to super-resolution grid. Optimization of particle image distortion is achieved by averaging a forward and a backward image distortion correlation for every iteration process. The proposed method is first verified by standard particle images of impinging jet flow that has exact solution available, and then applied to analyze uniform flow past two side-by-side circular cylinders. Satisfactory results are obtained from the jump matching scheme proposed. KEY WORDS: PIV; Optimization; Image distortion; Image interpolation
Hydrodynamics of trapezoidal embankment weirs
Xi-kun Wang 1*, Zhi-yong Hao 2 , Soon Keat Tan 3 1Maritime Research Centre
Nanyang Technological University, 50 Nanyang Avenue, Singapore 2Logistics Engineering College
Shanghai Maritime University, Shanghai, China 3School of Civil and Environmental Engineering, DHI-NTU Centre Nanyang Technological University, 50 Nanyang Avenue, Singapore
ABSTRACT: This paper presents the results of an experimental study over a 2-dimensional trapezoidal weir model with the upstream and downstream faces sloped at 1:2 (V:H). The flow field has been measured using Particle Image Velocimetry (PIV). Several hydrodynamic properties of the flow, including the different flow regimes, free surface profile, mean and instantaneous velocity fields, and discharge coefficient, are discussed and analyzed. KEY WORDS: weir, embankment, Particle Image Velocimetry (PIV)
Time-domain simulation of tank sloshing pressure and experimental validation
Shuo Huang, Wen-yang Duan , Xin Zhu
College of shipbuilding Engineering, Harbin Engineering University Harbin, China
ABSTRACT: In this paper, a time-domain Green function based BEM (boundary elements method) in presented to simulate tank sloshing problems. NURBS based higher-order panel method is developed to solve the boundary integral equation. To get physical real stable results, a modified tank wall boundary condition is presented. The model experiments were carried out using partially
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filled rectangular tank with forced sway motion. Sloshing-induced internal pressures and wave elevation have been obtained numerically and experimentally. It is observed that the present numerical methods provide a fair agreement with experimental results. Long-time simulations have also been carried out to demonstrate the stability of the method.
KEY WORDS: tank sloshing; incident wall damping; NURBS based higher-order panel method; time-domain
The hydrodynamic model for simulating the motions of a ship moored near the
quay in waves
Ming-chung Fang *, Bou-chaun Hsu , Joe-ming Yang
Department of Systems and Naval Mechatronic Engineering, National Cheng Kung University, Tainan, China
* E-mail: [email protected] ABSTRACT: In this study, a hydrodynamic mathematical model for simulating the motions of a ship moored near the quay in waves is presented. The related hydrodynamic coefficients such as the added mass, damping coefficient and wave exciting force are calculated by the two-dimensional source distribution method. The strip theory is then applied to integrate the whole ship hydrodynamic characteristics along the ship length and the ship motion behaviors in waves can be obtained through the equations of motions. The bank effects are treated by using the image method which is similar to the treatments of the twin hull ship except the differences on some coupled hydrodynamic forces. The time domain simulation technique is made to analyze the motions deeply by using the 4th order Runge-Kutta method. Different wave conditions are considered with respect to different clearances between the ship and bank and shallow water effect is neglected for simplicity. The present results will be helpful for the design on the ship mooring system arrangement near the quay or the wharf.
KEY WORDS: Hydrodynamic; bank effect; mooring; fender; tension.
Experimental and numerical investigations
on fast catamarans interference effects
Stefano Zaghi1, Riccardo Broglia1* , Andrea di Mascio1 1INSEAN - Italian Ship Model Basin, Rome, Italy
*[email protected] ABSTRACT: Experimental and numerical analysis of the interference effect for a fast catamaran is carried out. This work presents the status of an ongoing NICOP project, the focus is on the effect of the separation distance between the demihull on the performances as well as on the interference. To this aim, experiments and numerical simulations are performed for five different separation lengths (and for the monohull configuration) and for a wide range of Froude number (from 0.2 to 0.8). KEY WORDS: Catamaran, RANS based simulations, separation distance and interference.
Dynamic pressures on curved front seawall models under random waves
K. V. Anand*, V. Sundar , S. A. Sannasiraj 1Department of Ocean Engineering, Indian Institute of Technology
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ABSTRACT: The shoreline erosion is a major problem that persist world wide and seawall still remain as one of the most widely adopted coastal protection structure. The design of an efficient seawall should be such that overtopping is minimized even during coastal flooding and extreme events by maintaining its crest elevation as low as possible. This can be obtained with curved front face sea walls. Two such curved configurations have been chosen for the study. The experimental investigation on dynamic pressure variation along the surface of the seawall models placed over a bed slope of 1 in 30 and subjected to the action of random waves following the PM spectrum were conducted. The results on the variations of dynamic pressures on the seaward face of both the models along the relative depth are compared and discussed.
KEY WORDS: Seawall; pressures; non-overtopping seawall; Random waves.
Pressure distribution computed by wave-interaction theory for adjacent multiple bodies
Masashi Kashiwagi 1* , Qi-qi Shi 2
1Dept of Naval Arch & Ocean Eng, Osaka University, Osaka, Japan 2Dept of Naval Arch & Ocean Eng, Shanghai Jiao Tong University, Shanghai, China
ABSTRACT: In spite of a mathematical limitation that each interacting body must be far enough apart from the other bodies, the wave interaction theory has been used successfully even for a case where the separation distance between the bodies is virtually zero. Numerical investigation is made in this paper on the practical applicability of the wave interaction theory by considering four identical box-shaped bodies as a simplified example and comparing computed results with correct ones obtained by the higher-order boundary element method. It is shown that the wave force in the horizontal direction can be obtained favorably by the interaction theory even if the separation distance between the bodies is very small. To make reasons of this somewhat peculiar phenomenon clear, not only the integrated hydrodynamic force but also the pressure distribution on the body surface is calculated and compared with the results by the higher-order boundary element method. Discussion is made on whether the pressure is correctly obtained on the regions very close to adjacent bodies and fortuitous cancellation in the integration of the pressure occurs between the two vertical planes in close proximity. KEY WORDS: Wave-body interaction; multiple floating bodies; higher-order boundary element method; pressure distribution; integrated hydrodynamic force.
A new surface modification approach for CFD-based hull form optimization
Hyunyul Kim, Chi Yang *
Department of Computational and Data Sciences, George Mason University Fairfax,Virginia, USA
ABSTRACT: The main focus of this study is on the development of an efficient and effective hull surface modification technique for the CFD-based hull form optimization. Two approaches are utilized. One is based on the radial basis function interpolation, and the other the sectional area curve of the hull. Both local and global modifications of hull forms can be achieved by combining these two approaches. The hull surface modification technique developed in this study is used to vary the hull forms during the optimization process, in which the objective functions associated with the resistance is evaluated by a practical design-oriented CFD tool (SSF), and a multi-objective genetic algorithm is adopted to allow for multi-design speeds. For the purpose of illustration, the KRISO container ship (KCS) is taken as an initial hull to be optimized for reduced drag at given design speeds. Numerical results obtained in this study have shown that the present hull surface modification technique can produce smooth hull forms with reduced drag effectively and efficiently in the CFD-based hull form optimization. KEY WORDS: Hydrodynamic optimization; hull surface modification; hull form design; resistance; radial basis function.
ABSTRACT : The process of tidal bore passing through bridge piers is numerically simulated in an open channel using a pure Lagrangian method, i.e. Smooth Particle Hydrodynamics (SPH). Due to its “gridless” feature, SPH is intrinsically well-suited for the complex hydrodynamic simulation when the fluid encounters a structure. The behavior of bores propagation along the channel is illustrated herein and includes the bore’s free surface properties and flow field, and in particular, the intricate behavior of unsteady flow during the passage of tidal bore. The generation of shock waves between the structures can be clearly observed in the numerical experiment. Intense vortical structures behind the bore front are generated as the bore propagate through the constriction.
KEY WORDS: tidal bore, SPH, undular bore
Nonlinear analysis on wave-plate interaction due to disturbed vertical elastic plate
Guang-hua He 1* , Masashi Kashiwagi 1 1Department of Naval Architecture and Ocean Engineering, Osaka University,
ABSTRACT: Hydroelastic behavior of wave-plate interaction due to an initial deflection of a vertical elastic plate is simulated by using a Mixed Eulerian Lagrangian method for the fluid and a Finite Element Method for the plate. An implicit boundary-condition method is developed to solve the coupled motions of fluid and plate. A hybrid wave absorbing beach is installed to prevent the wave reflection from a vertical wall at the end of the wave tank. The 4th order Runge-Kutta scheme with uniform time step is used for time marching. First, numerical results of the elastic vibration of a vertical plate induced by deformation of itself at initial time are validated by comparing with corresponding analytical solution. Then, further comparison between the results from mode-expansion method and FEM is made. Finally, the influences of the edge condition at the top of plate and the plate stiffness on the wave-plate interaction are investigated systematically. KEY WORDS: Time domain; numerical wave tank; vertical elastic plate; BEM; FEM
Application of the adjoint method to the propeller designs
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the gradient methods are usually suffering from the inefficient computations of the gradients, and the adjoint method can remedy this problem. In this paper, the adjoint equation of the boundary element method is first derived, and it is then applied to the propeller design problems. The Lagrange-multiplier method with the adjoint equations for solving the gradients is used in this method. Two design examples are demonstrated in the paper, and both examples show that the presented method can successfully achieve the design goals. KEY WORDS: propeller design, optimization, adjoint method, boundary element method, Lagrange multiplier method
A numerical comparison of end-plate effect propellers and conventional propellers
Hsun-jen Cheng 1, Yi-chung Chien 1, Ching-yeh Hsin 1*, Kuan-kai Chang 2 , Po-fan Chen 3 1Department of Systems Engineering and Naval Architecture,
National Taiwan Ocean University, Keelung, China 2United Ship Design and Development Center, Taipei, China
ABSTRACT: Unconventional propellers with end-plate effects such as Kappel propellers get designers’ attention due to the environmental concerns and energy saving problems. The computations have been carried out to compare the Kappel propellers and the conventional propellers, and the emphasis is put on the scale effects and the structural performance. The scale-effect is first investigated, and the computational results show that the Kappel propeller has a larger scale effect than the conventional propeller. The structural analysis is then made, and the comparisons of the Kappel propeller and the conventional propeller show that the Kappel propeller suffers from a stronger stress concentration near the tip. KEY WORDS: end-plate effect, Kappel propeller, BEM, RANS, scale effect
Calculation of ship squat in restricted waterways by using a 3D panel method
Jian-xi Yao 1*, Zao-jian Zou 1,2 1School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, China;
2State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai, China *E-mail: [email protected]
ABSTRACT: A panel method is applied to calculate the sinkage and trim of a ship sailing in a shallow channel. The hull surface, free surface and channel wall surfaces are discretized into panels on which Rankine sources of constant strengths are distributed. An iterative scheme is used to deal with the nonlinear boundary conditions on free surface. The boundary condition on water bottom is satisfied by the method of images, whereas the radiation condition is satisfied by raised panels above free surface. The vertical force and pitching moment are obtained by integrating the hydrodynamic pressure over the hull surface, and the sinkage and trim are calculated according to dynamic equilibrium. Numerical calculations are performed for Series 60 (CB=0.6) ship. The numerical results are in good agreement with experimental data. KEY WORDS: sinkage; trim; panel method; shallow channel. Theoretical analysis of wave and structure interaction around a composite-type
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coastal structure - a case study of a seawall and detached breakwaters
Masato Ichikawa 1*, Takehisa Saitoh 2, Guo-ping Miao 3 1Nishimatsu Construction Co., Ltd, 1-20-20 Toranomon, Minato-ku, Tokyo 105-8401, Japan
2Department of Civil Engineering, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan 3School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, 1954 Huashan Road,
Shanghai 200030, China * E-mail: masato_ichikawa@ nishimatsu.co.jp
ABSTRACT: This study presents a theoretical method for analyzing flow fields around a composite-type coastal structure. A dividing region method, extended from previous work [1],[2],[3] is adopted, and the case composed of a seawall and detached breakwaters is the focus for a fundamental stage of this topic. Laboratory experiments are also conducted to examine the validity of this method. Theoretical results of water surface elevation around the composite-type structure agree well with the experimental results and the validity of this method is confirmed. KEY WORDS: Composite-type coastal structure; seawall; detached breakwaters; dividing region method, resonant phenomena.
RANS prediction of the KVLCC2 tanker in head waves
G.B. Deng1*, P. Queutey1, M. Visonneau1 1E.M.N, L.M.F-UMR6598, Ecole Centrale de Nantes
ABSTRACT: The present study is devoted to the computation of the KVLCC2 tanker in head wave with free heave and pitch motion. A RANS solver using finite-volume discretization and free-surface capturing approach is employed for the computation. Free ship motion is captured with a mesh deformation approach. Three different wave lengths (0.6Lpp, 1.1Lpp and 1.6Lpp) are computed. We focus on numerical uncertainty estimation in this paper. For each test case, three different meshes and at least three different time steps have been used to access both time and spatial discretization error. Additional computations with different setups aimed at identifying different numerical discretization errors will also be performed. It is demonstrated that special attention needs to be paid to time discretization. To keep the same time accuracy, time step needs to be reduced on fine mesh for such kind of unsteady free-surface computation involving important pitch or roll motion. KEY WORDS: Head waves; free-surface capturing; deforming mesh; pitch motion; uncertainty estimation
Numerical study of planing vessels in waves
Hui Sun * , Odd M. Faltinsen
Centre for Ships and Ocean Structures, Department of Marine Technology Norwegian University of Science and Technology
ABSTRACT: The performance of planing vessels in waves is investigated numerically by assuming linear regular incident waves in head sea. A 2D+t theory is presented to perform nonlinear time domain simulations of a prismatic planing boat in incident waves. A Boundary Element Method is employed to solve the initial boundary value problems in two-dimensional (2D) cross-planes. A simplified theory is also applied. The added mass and damping coefficients used in the latter theory are determined from the numerical simulation of forced oscillations. The wave induced heave and pitch motions calculated by these two methods are compared with the experiments by Fridsma [1].
ABSTRACT: A spatial non uniform inflow is the usual inflow to which a marine propeller is subjected to. Inside a ship wake, in inclined shaft condition, in tandem/contra rotating configurations, the spatial non uniformity of the incoming flow on the propeller plane leads to the unsteadiness responsible of thrust and torque fluctuations, induced pressures, cavitation and the associated noise. Any design method and, moreover, each analysis tool should be able to treat these phenomena, to carry out a more consistent ship oriented propeller design and to better understand the flow features and the performances of an already designed propeller. In the present work two different numerical approaches, a commercial RANS solver and a in house developed Panel Method, are addressed and applied for the analysis of marine propellers subjected to an oblique inflow, showing, through the comparison with the experimental measures, their capabilities and their limitations. KEY WORDS: RANS; Panel Methods; Unsteady Flow;
Three-dimensional modeling of tidal circulation within the north and south passages of the partially-mixed Changjiang River Estuary, China
John Z. Shi*, Chen Li, Xi-ping Dou 1
Department of Harbour and Coastal Engineering, State Key Laboratory of Ocean Engineering, School of Naval
Architecture, Ocean and Civil Engineering, The Shanghai Jiao Tong University, Shanghai , China 1Department of River and Harbour Engineering, Nanjing Hydraulic Research Institute, Nanjing , China
ABSTRACT: The COHERENS three-dimensional hydrodynamic model is used to simulate the barotropic tidal circulation within the North and South Passages of the partially-mixed Changjiang River estuary, China. Modeled surface elevation, current speed and direction have been validated against measured data during the spring, moderate, and neap tides in the dry season and flood season of 1996, respectively. Analyses of modeled results suggest that (i) tidal flow in the flood season showed stronger asymmetry than that in the dry season; and (ii) there was an apparent seasonal, spring/neap tidal and intratidal variability in tidal circulation within the North and South Passages. KEY WORDS: Numerical modeling; Mode splitting technique; Tidal flow field; the Changjiang River estuary
Design and analysis of counter-rotating propellers-comparison of numerical and experimental results
Davide Grassi1, Stefano Brizzolara2, Michele Viviani2, Luca Savio2, Sara Caviglia2
1ZF Marine Arco s.p.a. Arco (Tn), Italy
Email: [email protected] 2Department of Naval Architecture and Marine Engineering (DINAV),
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Email: [email protected] ; [email protected] ; [email protected] ; [email protected] ABSTRACT: In these last years a growing interest has been devoted to counter-rotating propellers especially for pod/stern drive applications for pleasure boats. In this context DINAV has been interested in the framework of an industrial R&D project to develop design/analysis computer codes for such kind of propulsors which is based on a modern lifting-line/lifting surface design method [1-4]. The present work is devoted to the comparison between the foregoing numerical design/analysis tools and the results of the cavitation tunnel tests. The validation study has been performed on a set counter rotating propellers designed to be installed on a commercial pod drive system.. Despite some uncertainty intrinsically connected to the nature of the test, results are very well in agreement with design points, allowing to validate the theoretical codes developed so far and to obtain semi-empirical correction factors for future application. KEY WORDS: contra-rotating, stern thrusters.
Turbulence structure of compound open-channel flows with one-line emergent vegetation
Michio Sanjou, Iehisa Nezu, Sohei Suzuki, Kota Itai
Department of Civil Engineering, Kyoto University, Katsura Campus, Kyoto, Japan * E-mail: [email protected]
ABSTRACT: Vegetation such as trees and shrubs are often observed at the floodplain edge in natural rivers. Spanwise profiles of streamwise velocity component are influenced significantly by the drag force of trees. That is to say, the streamwise velocity decreases locally behind trees and near the junction between the main-channel and the floodplain. This property is quite different from that observed in typical compound open-channel flows, in which the velocity profile has a single inflection point and forms a mixing layer related to large-scale horizontal vortices. In contrast, in compound open-channel flow with a one-line emergent vegetation, a “V“-shaped velocity profile appears with twin inflection points. It is thus very important to investigate these hydrodynamic properties and turbulence structure considering the emergent vegetation effects in river engineering and eco hydraulics. So, in the present study, turbulence measurements by 3-D acoustic Doppler anemometer (ADV) were conducted in 150cm wide laboratory flume, in which 2cm diameter and 25cm height cylinders are placed as vegetation models with 10cm span along the junction edge. KEY WORDS: Compound open-channel flow, emergent vegetation and 3-D ADV measurements
Lagrangian block hydrodynamics for environmental
fluid mechanics simulations
Lai-wai Tan, Vincent H. Chu*
Department of Civil Engineering and Applied Mechanics, McGill University Montreal, Quebec, Canada
ABSTRACT: The Lagrangian block hydrodynamics is formulated based on the block advection of fluid. By enforcing the mass and momentum conservations on the Lagrangian mesh, the numerical oscillation problem encountered in the classical Eulerian computational methods is circumvented. A large number of the previously computationally difficult problems in environmental fluid mechanics are successfully simulated using the method. Examples of these simulations are described in this paper.
ABSTRACT: Trees and shrubs observed in floodplain edge in natural rivers have significant impacts on hydrodynamic characteristics. In particular, spanwise profile of streamwise velocity component is influenced by the drag force of the trees, and consequently, the streamwise velocity decreases locally behind trees and near the junction between the main-channel and the floodplain. Furthermore, concentration exchanges such as nutrients between the main-channel and the floodplain differ from those observed in the non-tree compound open-channel flows. It is of essential importance to reveal how emergent trees influences these mass transfers. However, it is very difficult to evaluate time and space variations of the concentration by laboratory measurements. So, in the present study, a 3-D LES is used to overcome this difficulty, and we reveal the relation between the tree-alignment density and the exchange-rate of the concentration. KEY WORDS: Large eddy simulation, emergent vegetation and compound open-channel flows
Study on hydrodynamic and sedimentation problems in development of harbors located at offshore area with many islands and tidal channels
Shu-hua Zuo 1,2*, Bei Li 1 1. Key laboratory of Engineering Sediment of Ministry of Communications，Tianjin Research Institute of Water
Transport Engineering, Tianjin , China ; 2. State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, China;
*E-mail: [email protected] ABSTRACT: The Yangshan sea area which locates in the Qiqu Archipelago is a typical offshore area with muti-island and muti-channel. In this paper, taking Yangshan sea-area of the Qiqu archipelago as an example, a 2D numerical model of tidal currents and sediments is established to study the change of the current and sediment field. The validity of the model is verified by the observation data obtained in April, 2007 including the tidal flow and suspended sediment concentration in the vicinity of the harbor. The verification of calculation shows the calculated values are in good agreement with the measured data. The field of tidal currents, suspended sediment concentration and the seabed deformation can be successfully simulated. Finally, two layouts are simulated to study the changes of the current and suspended sediment field. And the seabed evolution is predicted with the model. Computational results show that the Branch Channel Layout is advantageous to the present situation. KEY WORDS: Offshore area; Yangshan deep-water harbor; Tidal currents; Suspended sediment concentration; 2D numerical model
Numerical simulation of sediment erosion by submerged plane turbulent jets
Wan-yun Xue 1*, Wen-xin Huai 1, Zhong-dong Qian 1
1State Key Laboratory of Water Resources and Hydropower Engineering Science,
ABSTRACT: Erosion of loose beds acted by submerged plane turbulent jets was simulated with the Eulerian two-phase model, which implements Euler-Euler coupled governing equations for fluid and solid phases. A modified κ-ε turbulence model was chosen to enclose the fluid phase. Both flow-particle and particle-particle interactions were considered in this model. The computational results were in a good agreement with previous laboratory measurements. The characteristics of the flow field in the two phases and the influences of hydraulic and geometric parameters on eroded bed profiles were analyzed based on the computational results. The calculational results reveal that: the Densimetric Froude number is the most important factor that influences the computational results of the eroded bed; sands may keep movable or still under the interaction among particles gravity, seepage force of pore water and friction between particles. And sands on the upwind side of the dune may be promoted along the water-sand interface to the sand mound by the local shear stress, which mainly influences the scoured shape; by adjusting the computational steps and methods, two problems in the Eulerian two-phase simulation are solved. KEY WORDS: Plane Jet Flow; Erosion; Numerical Simulation; Eulerian Model; Densimetric Froude number
Prediction of sediment transportation in deep bay (Hong Kong)
using genetic algorithm
F.X. Zhang1, Onyx W.H. Wai1 , Y.W. Jiang2 1Department of Civil & Structural Engineering, The Hong Kong Polytechnic University, Hong Kong
2Department of Ocean Environment, University of Xiamen, Xiamen, China *Corresponding author: Tel: +852 5131 0337, E-mail: [email protected]
ABSTRACT: The genetic algorithm (GA) is a powerful method which can be used to solve search and optimization problems. A genetic algorithm with tournament selection, uniform crossover and uniform mutation is used to optimize sediment transport parameters in this study. Two important parameters of sediment transport, the critical shear stress for deposition and resuspension, are optimized by GA. The results show that GA is efficient and robust for optimizing parameters of our sediment transport simulation of Deep Bay.
KEY WORDS: Sediment Transportation, Deep Bay, Genetic Algorithm.
Stochastic diffusion by progressive waves in turbulence
Adrian Wing-Keung Law1*, Siu-Kui Au2, Jie Song1
1School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Ave., Singapore 639798
2Department of Building and Construction, City University of Hong Kong, China 83 Tat Chee Avenue, Hong Kong
ABSTRACT : Pollutants that are chemically inert flow with the carrier fluid passively while diffuse at the same time. In this study, the diffusion behavior of passive pollutant in a progressive wave field with strong turbulence is examined with analytical means. The focus is on the nonlinear interactions between the stochastic diffusion and the deterministic wave-induced oscillatory advection. We limit our scope to cases whereby a small parameter, ε , exists between the advective and diffusive displacements, which then allows a perturbation analysis to be performed. With the sinusoidal progressive wave, the results show that the oscillating wave motion can either increase or decrease the stochastic diffusion depending on the wave characteristics. Longer wave lengths and shorter wave periods tend to promote diffusion, while shorter wave lengths and longer wave periods act in the opposite manner. The reinforcing effect is however much stronger than the diminishing effect. KEY WORDS: Stochastic diffusion, progressive waves, turbulence, perturbation analysis
Study on Bohai sea tidal dynamics under extratropical storm surge
1College of Harbor, Coastal and Offshore Engineering, Hohai University, Nanjing , China; 2 Nanjing Hydraulic Research Institute, Nanjing, China;
3 Key Lab of Ports and Waterway & Sedimentation Engineering Ministry of Communications, Nanjing , China;
4 Research Center for Climate Change, MER, Nanjing, China School or Company Affiliation * E-mail: [email protected]
ABSTRACT: Bohai Bay is one of the areas affected by by extratropical storm surges and the economy loss there due to this is remarkable. A numerical model is established to couple the astronomic tide and the storm surge for Bohai Sea and its vicinity. Based on validation, it is applied to analyse the influence of the extratropical storm surge in Oct. 2003 on the water level set-up/down and on the spatial-temporal variations of the flow fields. Due to the extratropical storm surge, the water level setup is obvious along the Bohai Bay coast; the water level fluctuation varies greatly. The tidal flow of Bohai Sea is changed from the local reversing tidal current to unidirectional flow. KEY WORDS: Bohai Sea; extratropical storm surge; flow field variation, numerical simulation
Velocity distribution of secondary currents in curved channels
Il Won Seo* , Young Jai Jung Dept. of Civil and Environmental Engineering, Seoul National Univ.
ABSTRACT: This research concerns steady secondary currents developing in open-channel bends and reviews the theoretical equations of the transverse velocity profile which have been developed by previous researcher. Rozovskii’s equation in which fully developed flow was defined at first contains function which is difficult to integrate analytically. Kikkawa et al.’s equation presents the characteristics of the section well. Baek et al’s equation reveals the stream-wise variations and the vertical profile of the transverse velocity. These existing equations are generally in good agreement with experimental results. However, equations didn't include exactly effects of flow resistance at water surface and bottom. Furthermore, no-slip condition was not considered. KEY WORDS: Secondary flow; Transverse velocity; Curved channel; Stream-wise variation; Vertical profile
Numerical simulation of the plug discharge under aerated condition
Ze-gao Yin 1*, Xian-wei Cao 1, Jin-xiong Zhang 2, Hong-da Shi 1 1 Ocean engineering key laboratory of Shandong province, Ocean University of China
Qingdao,China 2Department of Hydraulics, China Institute of Water Resources and Hydropower Research
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discharge under aerated condition. When flow enters the plug section, the gradient of air volume fraction increases much and varies drastically, and cavitation number decreases sharply and soon reaches the minimum. When flow enters the sudden expansion, air volume fraction and cavitation number increases respectively. With the increase of sudden expansion length, air volume fraction appears large at the top and small at the bottom and cavitation number increases to recover eventually. Cavitation number increases with the increase of air volume fraction. KEY WORDS: plug discharge; Fluent; air volume fraction; cavitation number.
Transitional gravity flow of sewers inappropriate entry
into storm drainage of a separate system
Hai-long Yin, Zu-xin Xu * State Key Laboratory of Pollution Control and Resource Reuse, Tongji University, Shanghai, China
ABSTRACT : Transitional sewer flows into storm drainage were measured in Caohejing drainage system of Shanghai, a separate system with inappropriate sewage entry into storm drainage. Flowing measurement demonstrated the limitation of Hazzen-William equation on quantifying the gravity flows in sewers, so an empirical formula was established. The dimensionless coefficient ranges from 0.34 to 16.38, representing supercritical flow under river water surging into one underground sewer culvert, and subcritical flow under normal gravatational free fall. Based on field investigation, it was known that the dimensionless coefficient under normal free fall is in the range of 0.34-4.17, and correspondingly gravatational velocity of sewers inappropriate entry into storm drainage ranges from 0.06 m/s to 0.71 m/s under investigated sewer water depth 1-5 cm. KEY WORDS: Transitional flow; dry-weather flow; gravity flow; swage; storm drainage.
Multiple tandem jet interaction in a crossflow
Adrian C.H. Lai1 , Joseph H.W. Lee1* 1Department of Civil Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong,China
ABSTRACT: We formulate a general semi-analytical model for multiple tandem jet interaction in a crossflow. For an array of buoyant jets arranging in tandem, the rear jets experience a reduced effective crossflow velocity due to the blockage and sheltering effect of the leading jet. The jet entrainment is modelled by a distribution of point sinks, and the blockage and sheltering effect is modelled by a distribution of doublets - both along the jet axis. The reduction of rear jet effective velocity as observed in previous experiments is successfully predicted by the model.
KEY WORDS: Jets and plumes; tandem jets in crossflow; multiple jet interaction; environmental hydraulics.
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Specification of wall boundary conditions and transverse velocity profile conditions in finite element modeling
Il Won Seo * , Chang Geun Song
Department of Civil and Environmental Engineering, Seoul National University, Seoul, Korea *E-mail: [email protected]
ABSTRACT: Present work mainly focuses on the influence of wall boundary conditions and imposition of transverse velocity boundary conditions on the flow field of a bluff body. Uniform velocity over the nodestring is specified in slip condition mode. Three types of transverse velocity profile are adopted for the no slip situation; top hat is same as slip case except for no velocities at wall; parabola for the simple and typical approximation of transverse velocity shape in open channel flow; beta distribution for the general expansion. Assignment of top hat and parabola velocity profiles yields maximum velocity nearby the cylinder while uniform one has maximum magnitude at side walls. Maximum velocity of parabola input is about 44 % higher than that of uniform assignment. KEY WORDS: wall boundary condition; transverse velocity boundary condition; slip condition; no slip condition; beta distribution.
Vertical 2-d mathematical model of sediment silting in dredged channel
Teng Wu 1*, Xiu-xia Li 2 1 College of Harbor, Coastal and Offshore Engineering, Hohai University, Nanjing , China
2 Nanjing Institute of Environmental Sciences, Ministry of Environmental Protection, Nanjing , China *E-mail: [email protected]
ABSTRACT: Channel excavation is an important project measure in channel dredging, which is widely applied in channel regulations. Since channel excavation changes the original channel’s bed morphology, the pattern of flow becomes more complicated and the relative balance between water flow and sediment is broken. The paper constructed a vertical 2-D numerical model of excavated channel focusing on the sediment deposition and flow distribution, which takes the hydrodynamic pressure into account and adopts auto-mesh technique. The model can effectively reduce the error caused by calculating meshes not completely matching with the calculating region. By introducing the hydrodynamic pressure, the mode can overcome the difficulty in modeling the severely changing velocity caused by the channel excavation. To verify the reliability of the model, Alfrin’s experimental datum is adopted in the paper, and the calculating results agree well with the experimental datum. KEY WORDS: dredged channel; vertical 2-D mathematical model; hydrodynamic pressure
Investigation of air-core vortex at hydraulic intakes
Ying-kui Wang1 , Chun-bo Jiang1* , Dong-fang Liang2 1State key laboratory of Hydroscience and Engineering, Tsinghua University, Beijing , China;
2Department of Engineering, University of Cambridge, Cambridge, UK *E-mail: [email protected]
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ABSTRACT: Hydrodynamic properties of the surface vortex have been investigated. Based on the Navier-Stokes equations, three sets of the new formulations for the tangential velocity distributions are derived, and verified against the experimental measurements in the literature. It is shown that one modification greatly improves the agreement with the experimental data. Physical model experiments were carried out to study the intake vortex related to the Xiluodu hydropower project. The velocity fields were measured using the Particle Tracking Velocimetry (PTV) technique. The proposed equation for tangential velocity distribution is applied to the Xiluodu project with the solid boundary being considered by the method of images. Good agreement has been observed between the formula prediction and the experimental observation. KEY WORDS: Air-core vortex, hydraulic intake, axisymmetric flow, PTV
Flow resistance in steep mountain rivers in Bolivia
Mauricio Romero1*, Nelson Revollo1, Johnny Molina1
1 Hydraulics Laboratory; Faculty of Science and Technology San Simon University, Cochabamba, Bolivia
ABSTRACT: The present paper illustrates the assessment of the Darcy-Weisbach flow resistance coefficients f at five steep mountain rivers located in the northern mountain range surrounding the city of Cochabamba in Bolivia. Extensive field works were carried out. Several empirical formulas were tested. Results show that some of the aforementioned formulas provide good results in the assessment of f, being the model of Ugarte & Madrid-Aris (1994) the most accurate one. Plots showing direct logarithmic relationships between f and the riverbed slope So were obtained for each studied river, as well as an overall relationship of f vs. So. KEY WORDS: Flow resistance; steep rivers; empirical formula
Simulation of storm surge for whole Pearl River Estuary with upriver runoff
Yun Bao *, Hong-yue Zou, Jie-bing Liu
Department of Mechanics, Sun Yet-sen University, Guangzhou510275, China
ABSTRACT: In this paper, the typhoon wind field is given by the Typhoon model. The simulation for the Pearl River estuary is nested with storm surge filed in the northern South China Sea. Using the two-dimensional hydrodynamic model ccost, the simulation model of the storm surge which considers the upriver runoff is established with the structured grid of the whole Pearl River estuary region. The landing process of the 0814 and 0915 typhoon which has great impact in the Pearl River Delta region in the recent years was simulated, and the comparison between the result of simulation and measured water level was given. It show that the storm surge model for the whole Pearl River estuary with the upriver runoff can better simulate the impact of storm surges in the whole Delta. The two huge eddies caused by the strong winds can be seen in the flow field of the Lingding estuary during the typhoon landing. KEY WORDS: storm surge; whole Pearl River estuary; upriver runoff
Swimming behavior of isolated ayu, plecoglossus altivelis altivelis,
ABSTRACT: Swimming behavior of isolated fish in running water has not been investigated. In this study, the swimming behavior of isolated ayu in the running water was recorded with a digital video camera with changing the velocity for five cases. The result showed that the swimming trajectory can be described by nodes and branches. It was found that the ground distance, swimming distance, ground speed and swimming speed in the streamwise direction increases with an increase of the flow velocity, because the ayu has positive rheotaxis. The turning angle of swimming trajectory decreases with an increase of the flow velocity. KEY WORDS: isolated ayu; node; branch; swimming distance; running water Comparison of wave fields caused by four proposed beach nourishment schemes
in Beidaihe, China
Cui-ping Kuang *, Lu-lu He, Yu Zhang, Yi Pan, Shu-gang Liu Department of Hydraulic Engineering, College of Civil Engineering, Tongji University
Shanghai, China Zhang Jia-bo, Yang Yan-xiong
Qinhuangdao Mineral Resource and Hydrogeological Brigade, Hebei Geological Prospecting Bureau Qinhuangdao, China
ABSTRACT: The erosion of west beach in Beidaihe has become severe in the recent years. In order to nourish the beach, four different engineering nourishment schemes are proposed. As a near shore project, wave is the main force in the sea area of west beach. Based on the information above, wave fields in the sea area of west beach under both ordinary wave condition (S, Hs=0.7m, T=3.2s) and strong wave condition (NE, Hs=1.5m, T=4.7s) are analyzed. The result shows that beach nourishment with two jetties and three submerged breakwaters protects the west beach most effectively. KEY WORDS: Beach nourishment; SWAN model; wave field; Beidaihe.
Hydraulics of discharge tunnel service gate: the flow regimes
A. Mohagheg, Jian-hua Wu
College of Water Conservancy and Hydropower Engineering, Hohai University, Nanjing , China, Email: [email protected]٭
ABSTRACT: During experiments which were conducted on a discharge tunnel laboratory model, bottom cavity beneath the free-falling nappe immediate downstream of the service gate was focused on. Three different flow regimes were detected each of which with particular features. The results provide a fair characterization of each flow regime. They highlight some differences between the limits of flow regimes in terms of dimensionless bottom cavity length and Froude number values under various step heights. The results also demonstrate that increase in step height at service gate provides more aeration in lower range of flow rates. KEY WORDS: Cavity length; discharge tunnel; flow regime; service gate.
Computational models for analyzing scouring problems at Nile River
Maged M. Elfiky , Abdelazim M. Negm , Talaat M. Owais, M. A Nassar *
Water & Water Structures Engineering Dept., Faculty of Engineering, Zagazig University, Zagazig, Egypt.
ABSTRACT: A computational model was used to estimate and analyze scouring problems at the Nile River. A partial failure of the upper slab of the lock guide pier upstream of the new Esmaeilia canal intake was observed. Therefore, the reach upstream of the new Esmaelilia canal 920 m long on the Nile River in front of Esmaeilia canal intake is considered in this paper. The hydrodynamic process has been calculated using a 2-D hydrodynamic model (HYD-2), which simulates the flow behavior in rivers. The sediment transport in the reach was simulated using a 2-D sediment transport model which has the capability of predicting the locations of scouring and silting along the considered reach. The use of the models was illustrated through the use of two alternatives solution to the problem.
KEY WORDS: Numerical model, scour, Nile River, sediment transport, Hydroinformatics.
Towards numerical prediction of unsteady sheet cavitation on hydrofoils
Da-qing Li *, Mikael Grekula, Per Lindell SSPA Sweden AB, Göteborg , Sweden
ABSTRACT: The paper presents a study of using a modified k-ω model to predict the unsteady cavitating flows around 2D and 3D hydrofoils in the framework of multi-phase mixture flow RANS approach. The cavitation is modeled by Schnerr-Sauer’s cavitation model. A 2D NACA0015 foil at cavitation number σ=1.0 (unsteady with cloud shedding) is studied first, followed by the Delft twisted 3D foil. It is found that the present RANS method is able to predict the essential features like re-entrant jets, the periodic shearing and shedding of cloud cavities. Two distinct shedding dynamics are noted for the 2D foil: (a) Shedding of medium to large scale structures (at low frequency); (b) Shedding of a series of secondary vortex cavities (at high frequency). For the 3D twisted foil, the collaborated effect of re-entrant jets from the curved closure line to break up a primary cavity, as well as the formation, roll-up and transport of cavitation vortices that are observed in the experiment are truly reproduced in the simulation. The method is found to have a tendency to under-predict the lift coefficients. KEY WORDS: cloud cavitation; shedding; turbulence model; cavitation model; hydrofoil.
Numerical investigation of unsteady cavitating turbulent flow
around a full scale marine propeller
Bin Ji 1, Xian-wu Luo 1*, Yu-lin Wu 1, Shu-hong Liu 1, Hong-yuan Xu 1, Akira Oshima2
1、State Key Laboratory of Hydroscience and Engineering, Tsinghua University
Beijing, China 2、Ship and Ocean Engineering Laboratory, Mitsubishi Heavy Industries
ABSTRACT: This paper treats the unsteady cavitating turbulent flow around a full scale marine propeller operated in non-uniform ship wake. The RANS method combined with k-ω SST turbulence model and the mass transfer cavitation model was applied for the flow simulation. It is noted that both the propeller performance and the unsteady features of cavitating turbulent flow around the propeller predicted by the numerical calculation agreed well with the experimental data. Due to the non-uniform wake inflow and gravity effect, there occurred periodical procedure for cavity development such as cavitation inception, growth, shrinking, etc near the blade tip for the propeller. The study also indicated that there was considerably large pressure fluctuation near the propeller during the operation. The 1st order frequency of pressure fluctuation predicted by numerical simulation equaled the rotating frequency of propeller blades. Both amplitude and frequency agreed with the experimental results fairly well. KEY WORDS: Unsteady cavitation; non-uniform wake; pressure fluctuation; full scale marine propeller
ABSTRACT: A compressible, multiphase, one-fluid RANS solver was developed to study turbulent cavitating flows. The interaction between turbulence and two-phase structures is complex and not well known. This constitutes a critical point to accurately simulate unsteady behaviours of cavity sheets. In the present study, different turbulence transport-equation models are investigated. Numerical results are given for a Venturi geometry and comparisons are made with experimental data.
KEY WORDS: Cavitation, RANS simulations, Homogeneous Model, Turbulence Model
The sensitivity of shallow mixing layers to upstream perturbations and its implication to numerical code validation
Man-yue Lam *, Hong-wei Liu, Mohamed Ghidaoui Department of Civil Engineering, Hong Kong University of Science and Technology, Clear Water Bay,
ABSTRACT: Unsteady numerical simulations (Unsteady RANS or Large-eddy simulation) of shallow mixing layers are gaining attention in researches. However, the fact that the development of shallow mixing layers is sensitive to upstream perturbations poses a challenge to the validation of numerical results against experiments. A valid question is that whether upstream perturbations should be simulated in detail so as to obtain numerical results directly comparable to experiments. In an attempt to answer the question, the paper studies the sensitivity of the downstream dynamics of shallow mixing layers to upstream perturbations. Simulations of temporal shallow mixing layers are performed with different types of initial perturbations, noting that initial perturbations in temporal simulations correspond to upstream perturbations in spatial simulations. Results suggest that although the initial development of vortices is known to be sensitive to initial perturbations, agreement is obtained for the energy spectra at large times when the difference in the perturbation forms is at large wavenumbers, because of the dissipation by both the bottom friction and the sub-depth scale eddy-viscosity. When the difference in the perturbation forms is at small wavenumbers, the difference in the initial development of large scale coherent structures is kept in the energy spectra at large times as the bottom friction causes the mixing layer stable after a certain time. It may imply that numerically simulated energy spectra at the downstream are comparable to experiments without simulating precisely the high wavenumber upstream perturbations, but low wavenumber perturbations should be well incorporated in modeling so as to obtain the correct dynamics of the large-scale coherent structures. KEY WORDS: shallow mixing layers, sensitivity, upstream perturbations, initial perturbations, initial development
Reduction of local scour at a bridge pier fitted with a collar
in a 180 degree flume bend (Case study: oblong pier)
3Khuzestan Science and Research Branch, Islamic Azad University, Ahwaz, Iran Email: [email protected]
ABSTRACT : Local scouring around the bridges pier occurs because of flow separation and developing several vortexes around the bridge pier. Such scour hole can cause failure of the bridge especially during the river floods. In this study, the use of oblong collars
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for reducing the effects of local scour at a bridge pier is presented together with the time aspect of the scour development. The study was conducted using in a 180 degree laboratory flume bend. Tests were conducted using one oblong pier in positions of 60degree under one flow conditions. In this study, the time development of the local scour around the oblong pier fitted with and without collar plates was studied. The effects of various sizes of collars fitted on the temporal development of scour depth at the oblong pier were also studied. The time development of the scour hole around the model pier with and without a collar installed was compared with similar studies on bridge piers. The results of the model study indicated that the maximum depth of scour is highly dependent on the experimental duration. It was observed that, as the size of a collar plate increases, the scour decreases. So minimum depth of scour is dependent on the 3D collar. KEY WORDS: Scour depth; Secondary flow; Collar; Oblong pier; 180 degree bend
Impact speed of vessel collision considering inland river channel characteristics
ABSTRACT: In this study, based on experimental evidence, the mechanical energy losses (ΔΗ) along two hydraulic inclined (angle φ, 0 8o oφ≤ ≤ ) jumps (d1, dm), namely the jump over a thin wall (w) and the jump over an abrupt step (w), are examined, compared and discussed, in the forms of ΔΗ/d1 and ΔΗ/H1, for a common field of w/d1 and angles φ. Two empirical equations for ΔΗ/d1 are presented and a number of diagrams as well, showing the differences in corresponding energy dissipation. The results of this investigation may help the hydraulic engineer when designing pertinent structures along open channel works.
KEY WORDS: Energy Losses; Jumps Over Thin Wall / Step.
Analysis of influence factors of cavity length in the spillway tunnel downstream of middle gate chamber outlet with sudden lateral
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ABSTRACT: For the aerator of sudden lateral enlargement and vertical drop at the outlet of middle chamber is taken as research object by the method of turbulent numerical simulation which is used to study the cavity length of spillway tunnel downstream of chamber. And there is reasonably good agreement between the numerical simulation and model tests results. The results show that, the distribution of adhesion spots along side wall varies according to the changing of aerator geometric dimension; changes of drop height or enlargement width have effect on both lateral and bottom cavity length; the bottom cavity length correlates closely to drop height and lateral cavity length has the most remarkable effect on enlargement width; under the same shape, both the lateral and bottom cavity grows longer with Froude number increasing, and the bottom cavity grows rapidly. KEY WORDS: Sudden lateral enlargement and vertical drop; Middle chamber; Bottom cavity; Lateral cavity; Correlation;
Study on external water pressure of water conveyance tunnel for the pumped storage power stations in Huizhou City∗
Yong Huang 1*, Zhi-fang Zhou
1Department of Earth Science and Engineering, Hohai University Nanjing, China
ABSTRACT: A 3D numerical model of groundwater flow is established according to the geological conditions. Fractured rock mass is consist of rocks matrix, which is represented using the equivalent continuum model and fracture network, which is described with a discrete-fractured network model. The two models are coupled with continuum groundwater table and flux equilibrium, and solution of coupling model is deducted. The comparison is conducted between the measured and simulated external water pressure, which shows that the coupled model is feasible. Also different drainage schemes are designed and discuss the distribution of external water pressure of the schemes. KEY WORDS: External water pressure; water conveyance tunnel; coupled model; fractured network.
Vortex-induced vibration on 2D circular riser using a high resolution numerical scheme
Jia-song Wang 1 , Hua Liu 1, Shi-quan Jiang 2, Liang-bin Xu 2, Peng-liang Zhao 3
1 School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, China; 2 CNOOC Research Center, Beijing, China;
3 Key Laboratory of Power Machinery and Engineering, Ministry of Education, Shanghai Jiao tong University, Shanghai, China
E-mail: [email protected] ABSTRACT: This paper presents a high resolution numerical method for vortex induced vibration (VIV) simulation on the fluid structure interaction (FSI) of circular cylinder which represents a two dimensional marine riser. For the VIV case, the cylinder is elastically mounted and is modeled as a spring-mass oscillation system. Based on a new proposed elemental velocity vector transformation (EVVT) method, a finite-volume total variation diminishing (TVD) approach developed recently for solving unsteady Reynolds Averaged Navier-Stokes (URANS) equation with the RNG turbulence model was used to simulate the key hydrodynamic parameters such as lift coefficients. The four-stage Runge-Kutta method is used to solve the dynamic response equation of the structure. The FSI prediction results are compared with the available experimental data and showed a good agreement in a wide range of Reynolds number, which provide a good picture of real physics of phenomenon including the Karman vortex streets with different vortex modes with regard to the reduced velocities. KEY WORDS: vortex-induced vibration (VIV)；fluid-structure interaction (FSI)；total variation diminishing (TVD); numerical simulation；Reynolds Averaged Navier-Stokes (URANS) equation
∗ Project supported by Program for Changjiang Scholars and Innovative Research Team in University under Grant (IRT0717), sponsored by SRF for ROCS, SEM(2009503512), Natural Science Foundation for Hohai University under Grant (2008433111) and Special funds to finance operating expenses for basic scientific research of Central Colleges.
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On the gas leakage way of supercavity and vehicle vibration
Jing-jun Zhou 1*, Kai-ping Yu, Ming Yang , Xiao-hui Wan 1 School of Aeronautics, Harbin Institute of Technology, Harbin, China
* E-mail: [email protected] ABSTRACT: Steady and unsteady three-dimension numerical simulations were carried out to ventilated supercavitation by solving Navier Stokes equations with finite volume method based on the two-fluid multiphase flow model and SST (Shear Stress Transport) and DES (Detached Eddy Simulation Model) turbulence model were adopted respectively. The cavity developing process with re-entrant jet flow and two vortex tube gas-leakage way were studied and the change curve of pressure at a fixed point in cavity with time was given. On the other hand, the dynamics equation combined with moving technology was used to control the oscillation of the vehicle in the cavity, the change law of drag, lift, velocity as well as the displacement were given and analyzed.
Numerical simulation of the water-entry of body based on the Lattice Boltzmann method
Ke Zhang 1*, Kai Yan, Xue-sen Chu, Guan-yi Chen
1 China Ship Scientific Research Center, Wuxi, China * E-mail: [email protected]
ABSTRACT: In this paper, a lattice Boltzmann single-phase model is implemented to the simulation of the process of body entering water vertically. The initial water-entry process of a two dimensional cylinder and the process of a three dimensional disk entering water vertically at constant speed is simulated. The deformation of free surface and the relationship between the relative closure depth of water-entry cavity of the disk and the Froude number is studied. It is demonstrated that the LBM single-phase method is applicable to the water-entry problems. KEY WORDS: numerical simulation; lattice Boltzmann method; water-entry; free surface .
Numerical simulation of water-exit
of a cylinder with cavities
Xue-sen Chu 1*, Kai Yan, Zhi Wang, Ke Zhang, Guang Feng, Wei-qi Chen 1 China Ship Scientific Research Center, Wuxi, China
* E-mail: [email protected] ABSTRACT: The water-exit process of a cylindrical body was simulated in this paper. In the simulation, cavities were formed on the nose and at the tail of the body when the body approaches to the free surface, and then collapsed during the passage of body through the water surface. The interaction of free surface with cavity were simulated, and the high pressure due to collapse of cavities were captured. KEY WORDS: Water-exit; cavitation; numerical simulation.
A short review on the homotopy analysis method in fluid mechanics
Sh-ijun Liao
State Key Lab of Ocean Engineering, Shanghai Jiaotong University Shanghai , China
Project support by the major National Natural Science Foundation of China(Grant No 10832007
ABSTRACT: We give a short review on the current development of homotopy analysis method (HAM), an analytic technique for strongly nonlinear problems, and its applications in fluid mechanics.
ABSTRACT : In this paper, the ship lock entry problem is studied, which is physically similar to, but numerically different from, the water entry problem simulated by the author 25 years ago under the instruction of Prof. He. A one-dimensional unsteady hydraulic narrow-channel model for the flow coupled to the ship's motion in surge, heave and pitch is formulated and numerically implemented. The calculated ship motions were validated by comparison with model experiments carried out in the Duisburg shallow water tank. The viscous effects are further taken into account in order to investigate the scale effect in the experimental modeling in a framework of new lock project of Panama Canal. Thus, the experimentally validated model is applied to optimize the lock entry time by changing the trust course in the full-scale case.
KEY WORDS: Water entry; ship lock entry; free surface motion; ship motion; dynamic fluid-rigid body coupling.
Numerical study of the cavitating flows over underwater vehicle with large angle of attack*
Ying Chen 1*, Chuan-jing Lu 1, 2, Jian-hong Guo 1 1Department of Engineering Mechanics, School of Naval Architecture, Ocean and Civil Engineering, Shanghai
Jiaotong University, Shanghai, China 2State Key Laboratory of Ocean Engineering, Shanghai Jiaotong University, Shanghai, China
ABSTRACT: A Homogenous-Equilibrium-Model based cavitation code was developed to numerically analyze the three-dimensional cavitating flows over underwater vehicle navigating with large angle of attack. Rayleigh-Plesset equation based cavitation model was used together with non-linear eddy-viscosity turbulence model. The computed cavity shapes and pressure distributions along the vehicle body were found to generally accord with experimental results at different cavitation numbers and angles of attack. The forces acting on the vehicle body was studied qualitatively to explain why the body may get damaged during navigation. It was also discovered interestingly that, the variation trend of drag-force along with cavitation number at the conditions of large angle was completely opposite to that at zero angle. KEY WORDS: cavitation; numerical; angle of attack; cavity shape; pressure; force coefficient
Numerical study of periodically forced-pitching of a supercavitating vehicle *
Zhan-cheng Pan 1*, Chuan-jing Lu 1, 2, Ying Chen 1*, Shi-liang Hu 1* 1Department of Engineering Mechanics, School of Naval Architecture, Ocean and Civil Engineering,
Shanghai Jiaotong University, Shanghai, China Project supported by the National Natural Science Foundation of China (Grant No: 10832007) Biography: CHEN Ying (1979-), Male, Ph. D.
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2State Key Laboratory of Ocean Engineering, Shanghai Jiaotong University, Shanghai, China * E-mail: [email protected]
ABSTRACT: The unsteady behaviors, such as surging, heaving and pitching motion, which often occur during the advancing of supercavitating vehicle, has significant effect on the stability of supercavitaty and the trajectory of the vehicle. This paper presents a 3-dimentional numerical simulation of periodically forced-pitching of supercavitating vehicle. Based on the finite volume method and the pressure-based segregate algorithm, in the framework of Mixture multiphase model, associated with dynamic mesh method, the Reynolds-Averaged Navier-Stokes equations are solved for the ventilated cavitating flow field in a cavitation tunnel. For both steady-state and dynamic cases, the numerical results agree with the experimental results very well. When the vehicle is pitching periodically, the profile of the supercavity doesn’t vary significantly. The pressure inside the cavity fluctuates slightly during the pitching motion, while the pressure fluctuates significantly at the rear of the down-line of the vehicle. The hydrodynamic forces of the vehicle oscillated periodically, but not linear related to the pitching motion. KEY WORDS: supercavitating; numerical; dynamic mesh; pitching.
Simulation of unsteady artifiсial supercavities
Guang Feng 1*, Wei-zheng Chen, Xue-sen Chu, Zhi Wang, Ming-hui Zhang, Wei-qi Chen 1 China Ship Scientific Research Center, Wuxi, China
* E-mail: [email protected] ABSTRACT: The ventilated cavity in acceleration process for a supercavitating vehicle was simulated in this paper based on the independent expansion principle of cavity section. The unsteady artificial super-cavities were simulated under the condition of a straight navigation at the fixed depth. The hydrodynamic schemes of gas leakage from the cavity, the gravity effect and the angle of attack of the cavitator were taken into account in the simulation. By calculation for the supercavity of the acceleration process, a good ventilating rule was summarized as follows: a large ventilating rate lasts about 0.3s, then the ventilating rate should be reduced to the rate corresponding to the cruising state. KEY WORDS: supercavity, acceleration process, ventilation
Application of SPH method on free surface flows on GPU
Ben-long Wang, Hua Liu Engineering Mechanics, Shanghai Jiao Tong University
ABSTRACT: A parallel SPH solver is developed using GPU for free surface flows. As a kind of Lagrange methods, fluid particles are tracked by integrating the momentum and kinematics equations. Mass conservation is automatically satisfied. Therefore SPH is suitable for simulating the flows with complex free surface. With this 3D flow solver, flows after dam-breaking are simulated with good performance using GPU. KEY WORDS: SPH; Free surface flows; GPU.
Rheological characterizations and extrudate swell predictions of an LDPE melt
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by two KBKZ-type constitutive equations∗
Shu-xin Huang 1, Xin Chen 1, Chuan-jing Lu 1, Zong-lin Peng 2, Chu-rui Wan 1, Xiao He 1, Mu-xin Sun 1
1 Department of Engineering Mechanics, Shanghai Jiao Tong University, Shanghai, China 2 School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai, China
ABSTRACT: The shear viscoelastic properties of an LDPE (1I2A-1) melt at 160 ℃ were described by using two KBKZ integral type constitutive equations, i.e. Wagner model and the three- parameter rational type model. The present characterizations were compared with the previous calculations by using PSM model. The results show that there are differences between the descriptions on the stress relaxation property in step strain and the first normal stress difference for the three models, and however, all the three models show the almost same predictions on the shear-thinning viscosity of the ldpe melt. Both Wagner model and PSM model are good choice in describing the rheological properties of the melt due to theirs simplicity. The Tanner theory combined with the Wagner model or the three-parameter rational type model was used to predict the swell ratio of the LDPE melt through a long capillary die, which was also compared with the experimental results and the previous calculations on swell. The predictions by Tanner theory combined with the three different constitutive models on the swell ratio of the LDPE melt are similar, which are apparently lower than the experiments and numerical simulations over the whole experimental shear rate range. The results further indicate that Tanner theory cannot predict the swell ratio of the LDPE melt precisely. KEY WORDS: LDPE; extrudate swell; viscoelastic properties; KBKZ-type models; Tanner theory
Orientation distribution and rheological properties of fiber suspensions flowing through curved expansion and rotating ducts
Qi-hua Zhang 1, Jian-zhong Lin 1,2* 1School of Aeronautics and Astronautics, Zhejiang University, Hangzhou, China;
2China Jiliang University, Hangzhou, China * E-mail: [email protected]
ABSTRACT: In dilute fiber suspensions, the Jeffery equation is employed to predict the fiber orientation distribution through a curved expansion and rotating duct. The results show that the fiber flips more quickly in the inlet region, especially in the region close to the concave wall. In the central region and the downstream region, the fiber orientation distributions are more uniform. In semi-dilute fiber suspension, the fiber interactions can be represented by a statistical model developed by Folgar & Tucker. Then a deduced Fokker-Planck equation can be used to describe the fiber orientation distribution probability. In the present work, the Fokker-Planck equation is directly solved by FVM. Then with the probability, the fiber orientation tensors are obtained. Furthermore, the fiber extra stresses are gained with the Batchelor model. The results show that the shear stress and normal stress difference are concentrated around the inlet close to the concave wall regions. In the central regions, these properties are less obvious. And in the downstream, these properties are negligible. KEY WORDS: fiber suspension; orientation distribution; Jeffery equation; Fokker-Planck equation; rheological property; curved expansion; rotating duct.
Simulation of acoustic scattering by the fast BEM approach
Zai-you Yan Department of aerodynamics, Nanjing University of Aeronautics & Astronautics, Nanjing, China
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ABSTRACT: Boundary element method accelerated by the precorrected-FFT (pFFT) algorithm is developed and implemented for acoustic scattering problems. Because models with very fine meshes can be computed using this method, high frequency responses can be simulated. In the implementation, constant triangular elements are applied. An example of a plane acoustic wave scattering by a rigid sphere is simulated to validate the in-house fast BEM code for acoustic scattering problems. Numerical results are compared with the corresponding analytical solutions and the solutions by the conventional boundary element method. As a result, the pFFT accelerated boundary element method greatly improve the computational efficiency and reduce the requirement of storage largely. The accuracy by this method is comparable to that by the conventional boundary element method as the grid-order is no less than 4. KEY WORDS: Boundary element method, pFFT, acoustic scattering, plane acoustic wave.
Tunnel hood effects on high speed train-tunnel compression wave
Xin-tao Xiang, Lei-ping Xue *
School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University Shanghai China
* E-mail : [email protected] ABSTRACT: This paper reports the numerical research of tunnel hood effects on high speed train-tunnel compression wave. The three-dimensional simulation with real geometry is carried out by the implementation of a commercial computational code. The train speed is 350 km/h. The train/tunnel blockage ratio is 0.115. Nine different types of tunnel hoods were studied. The calculation results showed that the hood length, the hood cross sectional area and the ventilation holes might have significant influence on the first compression wave, and inclined entry or asymmetric distribution of the ventilation holes is not available for alleviating the impulsive wave. KEY WORDS: high speed train; tunnel hood; compression wave; impulsive wave.
Verification and validation for RANS simulation of KCS container ship without/with propeller
Zhi-rong Zhang 1* 1China Ship Scientific Research Center, Wuxi, China
ABSTRACT: The free surface flow of a modern container ship KCS without propeller was firstly simulated using three sets of grids. The computed results including resistance, wave elevation and flow field on propeller disk were compared with the experimental data in detail. Verification and validation of resistance and wave profile were performed using recommended procedures proposed by ITTC. Then the viscous flow around KCS with operating propeller behind was also simulated. Both body force approach and sliding mesh approach were applied to consider for the effect of propeller. The results of these two approaches were compared with the measured data. These numerical investigation shows that accurate prediction of propeller/hull interaction using CFD method is becoming feasible and the huge potential of CFD application in ship hydrodynamics performance prediction is demonstrated.
ABSTRACT: The massive separating flows around landing-gear-like configurations, such as Rudimentary landing gear (RLG) and tandem cylinders (TC), are calculated using unsteady Reynolds averaged Navier-Stokes (URANS) and delayed-detached-eddy simulation (DDES) based on k-ω-SST model. A number of numerical schemes and dissipation are applied in an effort to compare the averaged as well as the instantaneous flow-fields with the available measurements. It is shown that high-order and low-dissipation scheme is necessary to calculate the small scale structures. Furthermore, DDES delivered better results than URANS. KEY WORDS: massive separation, RLG, TC, DDES, numerical scheme and dissipation
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ABSTRACT: Tsunami increases its height on the shallow water area and may transfers into bore when it breaks. Bore type tsunami sometimes produces huge forces and causes large damages on coastal infrastructures. In order to mitigate tsunami damages, bore type tsunami propagation, run-up and its characteristics need to be understood. And aside of experimental study, numerical simulation provides principal physical quantities with higher resolution in time and space. This study discus the validity of a numerical simulation based on VOF method, CADMAS-SURF, and characteristics of bore propagation on to a dike. KEY WORDS: Bore type Tsunami; Tsunami inundation; VOF method; CADMAS-SURF; Wave force.
Towards a fully 3D domain-decomposition strategy for water-on-deck phenomena
Giuseppina Colicchio1,2* ,Marilena Greco1,2,3 ,Claudio Lugni1,2 ,Odd Magnus Faltinsen1,2,3 1INSEAN, The Italian Ship Model Basin, Rome, Italy
2CeSOS, Center of Excellence for Ships and Ocean Structures, Trondheim, Norway 3Department of Marine Hydrodynamics, NTNU, Trondheim, Norway
ABSTRACT: A numerical approach has been used to analyze the water shipping caused by head sea waves for a FPSO ship at rest. A 3D Domain-Decomposition (DD) strategy is used, where a linear potential-flow seakeeping analysis of the vessel is coupled with a local nonlinear rotational-flow investigation for the prediction of water-on-deck phenomena. The Navier-Stokes solver is applied in the region close to the ship bow. It combines a finite-difference spatial algorithm with a predictor-corrector time scheme. The sea and ship surfaces are tracked with a Level-Set (LS) technique and a hybrid Eulerian-Lagrangian algorithm. The inner solver receives the initial and boundary conditions in terms of velocity, pressure, sea-surface location and ship motions and provides the loads due to the nonlinear wave-ship interaction (including green-water loads) to the seakeeping method. Here the inner solver and its implementation within the DD are described in detail. Preliminary results in terms of water-on-deck occurrence are discussed and compared against 3D water-on-deck experiments. KEY WORDS: Domain decomposition; level set; hybrid technique; FPSO; water on deck.
Numerical simulation of the structure of propeller’s tip vortex and wake
ABSTRACT: By means of numerical simulation, the evolvement of tip vortex and vortical trailing wake of a propeller were studied in details. From upstream of leading edge up to downstream of trailing edge, the tip vortices region extends rapidly and becomes sizable, which reason is that the transport of vortices between trailing wake and tip vortex takes place. The trailing wake region or the tip vortex region, each consists of sub-regions. The direction of the vortices in one of the sub-regions is opposite to that of the other sub-region. Each sub-region is structured with vortex layers of varying strength. The trailing wake possesses significant thickness and the tip vortex region occupies sizable space. The present analysis also show that within certain distance downstream from tailing edge, although the size and the configuration of the vortices region varies with going backwards, the total vortices flux through each station almost remains constant. KEY WORDS: Tip vortex; wake of propeller; CFD
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A comparative study on the fatigue life of mooring systems with different composition
Jun Sik Han 1*, Yun Ho Kim 1, Young Jun Son 1, Hang S. Choi 1 1Department of Naval Architecture & Ocean Engineering, Seoul National University
Kwanak-ro 599, Sillim-dong, Kwanak-ku, Seoul, Korea * E-mail: [email protected]
ABSTRACT: In this paper, two different types of the mooring system for a FPSO are considered, which is supposed to be installed in Gulf of Mexico. One system consists of 16 mooring lines (four by four) and another one consists of 12 mooring lines (four by three). It is designed that the static system stiffness are almost the same. Then two mooring systems are analyzed from the viewpoint of the extreme load and the fatigue life. A time-domain computational code is used in order to determine the extreme tension, while the spectral method is implemented for estimating the fatigue life. In the extreme dynamic load case, two mooring systems have almost the same results. In consequence, the fatigue life differs only
slightly.
KEY WORDS: fatigue; mooring; chain; FPSO
A study on the sloshing effect on the motion of 2d boxes in regular waves
Dong-young Lee 1*, Hang S. Choi1, Odd M. Faltinsen2 1Department of Naval Architecture and Ocean Engineering, Seoul National University,
Kwanak-ro 599, Sillim-dong, Kwanak-ku, Seoul 151-744, Korea 2Department of Marine Technology, Norwegian University of Science & Technology,
ABSTRACT: In this paper, we present a fundamental study on the sloshing effect for the sway motion of two boxes in two dimensions. First, we carry out experiments for two boxes of the same size and also different size in regular waves with different filling ratios, where the boxes are firmly connected each other. The sway motion is measured by a non-contact video camera. The measured motion is compared with numerical results obtained by using a computer program constructed based on the single-dominant multi-modal method. Good agreements are in general found, but clear discrepancies can also be observed at some incident wave frequencies. The friction on the tank rail and the locally resonated fluid motion between two boxes are regarded as main error sources. Therefore, it is necessary to clarify these error sources to predict more accurately. KEY WORDS: Sloshing; Two tanks; Ship motion; Experiment; Multi-modal method
Verification and validation of CFD predictions for a manoeuvring tanker
Lu Zou 1*, Lars Larsson 1 ,Michal Orych 2 1Department of Shipping and Marine Technology, Chalmers University of Technology
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ABSTRACT: This paper presents a study on the Verification and Validation (V&V) of CFD solutions for a tanker without appendages manoeuvring at varying drift angles and water depths. A steady state Reynolds-Averaged Navier-Stokes solver is applied to solve the viscous flow around the ship neglecting the free surface, sinkage and trim. Discretization errors and uncertainties in hydrodynamic forces and moments are estimated through grid convergence studies. Validation is performed by comparison with model test data. KEY WORDS: Ship manoeuvring; drift; shallow water; discretization error; uncertainty
Numerical simulation of a submerged gravity cage with the frame anchor system in irregular waves
Yun-peng Zhao *, Tiao-jian Xu, Guo-hai Dong, Yu-cheng Li
State Key Lab of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, China
ABSTRACT: When typhoon or extreme wave conditions occur, submergence under water may be an effective way for the net cage to avoid the attack. In this paper, a numerical method is developed to simulate the hydrodynamic behavior of net cage, which has been verified in our previous paper. Herein, by the numerical model the mooring line force and cage motion are calculated when the net cage is both in floating and submerging conditions. According to the simulated results, it can be found that the decrease of the mooring line force and cage motion is obvious when the net cage is submerged. The results of this study will give a good reference for better knowledge of dynamic behavior of submersible net cage. KEY WORDS: Gravity cage; numerical simulation; wave forcing; spectrum analysis
Prediction of excess resistance of ships by 3-D near field approach and its
comparison with some alternative methods
N.M. Golam Zakaria1 , Mir Tareque Ali
Dept. of Naval Architecture and Marine Engineering Bangladesh University of Engineering and Technology(BUET), Dhaka-1000, Bangladesh
ABSTRACT: Second-order forces have been widely investigated using 2-D methods since the early 60’s and more recently also using 3-D methods. The present work uses near field approach of 3-D Green Function method as well as some alternative 2-D methods for calculating the second order forces or excess resistance in waves. In this paper, results for excess resistance using both 3-D near field approach and 2-D methods are presented and compared with other published data and experimental measurement. The application of present 3-D approach to sea keeping problems of some complex geometry like Series 60 hull and a bulk carrier ship demonstrates that 3-D near field approach is valid in predicting added resistance of ship in waves and also provides better results in many cases particularly for blunt shaped slow speed vessel. KEY WORDS: Second order force, Ship motion, Near-field approach, Momentum conservation method.
Numerical simulations of wave-induced ship motions in regular oblique waves
ABSTRACT: Based on the method for ship motions in head waves, the numerical method for predicting ship motions in oblique waves is developed in this paper. The artificial spring model is adopted to control the numerical drifting in sway and yaw motions, while the empirical method is used for roll damping due to viscous effects. To validate present method, the simulated results of Flokstra container in oblique waves are compared with the experimental results. KEY WORDS: Panel method; time domain; ship motions; oblique waves; roll damping; artificial spring.
Roll response of ship-hull sections in variable bathymetry regions
by a hybrid BEM- vortex particle method
Kostas A. Belibassakis
Department of Naval Architecture, Technological Educational Institute of Athens Ag. Spyridonos 12210, Athens, Greece
ABSTRACT: A non-linear, hybrid method has been developed with application to the problem of roll response of ship-hull sections of general shape, floating in general bathymetry regions. Using domain decomposition, the present method is based on boundary element formulation for the representation of the non-linear potential wave motion around the floating body, in combination with vortex particle method for the generation of vorticity in the boundary layer and numerical simulation of vorticity convection and viscous diffusion in subregions close to the solid boundary. Subsequently, hydrodynamic forces on the floating body are obtained by pressure integration, and the hydrodynamic coefficients (added mass, damping) are calculated. Numerical results are presented and compared with experimental data and other methods. It is shown that the present method provides results of reasonable accuracy, illustrating that the mixing of boundary integral methods and particle methods is a useful tool for the evaluation of ship-hull characteristics in rolling motion, where viscous effects associated with boundary layer separation could be significant. KEY WORDS: floating body; general bathymetry; rolling motion; hybrid BEM, vortex particle method
Analysis of oil-lubricated herringbone grooved journal bearing with trapezoidal cross-section, using a spectral finite difference method
Jun Liu *, Mochimaru Yoshihiro**
*Tochigi R&D Center, Keihin-Corp, 2021-8, Hoshakuji Takanezawa-machi,Shioya-gun, Tochigi, Japan **Department of International Development Engineering, Graduate School of Science and Engineering, Tokyo
ABSTRACT: A modified Reynolds equation for an oil-lubricated journal bearing is derived, including curvature effect under a lubrication theory, and the curvature effect on characteristics of the journal bearing is discussed. In addition, in case of a herringbone-grooved journal bearing with trapezoidal cross-sections, the modified Reynolds equation is solved, using a spectral finite difference method to get characteristics such as variation of load capacity and attitude angle for trapezoidal angles of from 1.8 through 7.2 degrees. KEY WORDS: fluid lubrication, modified Reynolds equation, curvature effect, herringbone grooves, trapezoid groove, journal bearing
Applied new rotation correction κ ω− SST model for turbulence simulation
ABSTRACT: Based on the analysis of transportation equation of turbulence fluctuant velocity in the rotating frame of reference, it is the first time that the extended intrinsic mean spin tensor is instead of mean vorticity tensor in the well-known Richardson number and applied to improve the A.Hellsten`s correction of system rotation to Menter`s κ ω− SST turbulence model. The modified model is more applicable for turbulence simulation in the rotating frame of reference. It is used for turbulence simulation of flow in the centrifugal pump impeller in this paper. Compared with Menter`s κ ω− SST and original rotation correction, this model can get better result of effect of system rotation and its induced to the turbulence in the centrifugal impeller. KEY WORDS: turbulence model, rotating frame of reference, extended intrinsic mean spin tensor.
1On studies of formation, diffusion mechanisms and prevention measures
of CO during HEGF in low permeability oil reservoirs
Chun-sheng Pu 1,2* , Peng Rao 1,3, Min Zhou 1, Fei-peng Wu 1 , Wen-long Qin 2 1 School of Petroleum Engineering, China University of Petroleum, Dongying, China
2 School of Petroleum Engineering, Xi’an Shi You University, Xi’an, China 3 Qinghai Oil Field, CNPC, Dunhuang, China
ABSTRACT : High energy gas fracture（HEGF）has been one of central measures used to increase production and effusion in low permeability reservoirs. But there are some problems of this technology. One of them is that large number of toxic and harmful gases caused by it will trigger severe CO poisoning events. In this paper, the formation-gathering rule and countermeasures of CO for HFGF were studied across-the-board in low permeability reservoirs. The study showed that the primary reasons to produce CO are HEGF itself and that high temperature gases for HEGF reacted with associated gas and oil. At the same time, the formation mechanism of CO was illuminated. The study was of great theoretical value to prevent CO in effect for low permeability reservoirs, and was of great guiding significance for the rational development of similar oilfields. KEY WORDS: High energy gas fracture; CO formation mechanisms; prevention measures
A study on separation performance of a vortex finder in a liquid-liquid cylindrical cyclone
Shi-ying Shi, Ying-xiang Wu, Jun Zhang, Jun Guo, Shu-jing Wang
Institute of Mechanics, Chinese Academy of Sciences, Beijing , China *E-mail: [email protected]
This work was supported by a grant from the project of China Natural Science Foundation (50774091) , the National scientific research project of China (2005BA901A13, 2008ZX05002).
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错误！未找到引用源。ABSTRACT: This paper outlines the influence of design parameters such as different diameter, different shapes and insertion depth of a vortex finder on Liquid-Liquid Cylindrical Cyclone (LLCC) oil-water separation characteristics through experiments and numerical simulations. Through numerical simulations, the separation efficiency for water-dominated flow conditions is obtained and the results show that there exists an optimal shape, diameter and insertion depth of a vortex finder in cylindrical cyclones under certain conditions. In our laboratory, a 100mm inner diameter LLCC is adopted to test the influence of different insertion depths of the vortex finder and the results again indicate that an optimal insertion depth exists. The numerical results agree well with the experimental data of Rajkumar S et al. . So numerical simulations can be used to predict the complex flow behavior, the separation efficiency in a LLCC for optimizing the structure and provide some design guidance for their industrial application as the oil-water separators on offshore platforms and oil field inland. KEY WORDS: Liquid- Liquid Cylindrical Cyclone; vortex finder strucure; oil-water separation; experiment; numerical simulation.
The numerical and experimental research on unsteady cloud cavitating flow of 3D elliptical hydrofoil
Deng-cheng Liu *, Fang-wen Hong, Fang Lu
China Ship Scientific Research Center, Wuxi, China *E-mail: [email protected]
ABSTRACT: Using Singhal’s full cavitation model and a modified k–ε RNG turbulence model, the unsteady cavitating flow and the dynamic shedding of cloud cavitation from the 3D elliptical foil were numerically investigated. For validating the simulation result, the corresponding experiments were carried out in cavitation tunnel at CSSRC. The modification of turbulence model made to the turbulence model addresses the influence of compressibility effect on turbulence by artificially modifying the turbulent viscosity and takes effect only in the compressible mixture flow region. The main features of cloud cavitating dynamics shedding agree well with the experimental observations. KEY WORDS: 3D elliptical hydrofoil, Cloud cavitation, Numerical and experimental research
Experimental investigation and numerical prediction of cavitation incurred
on propeller surfaces
Yu-chi Chang 1, Chin-ning Hu 1, Jing-chin Tu 2, Yi-chih Chow 1*
1Department of Systems Engineering & Naval Architecture National Taiwan Ocean University, Keelung,China
2United Ship Design & Development Center Tamshui, Taipei, China
ABSTRACT: Multiple types of cavitation appearing on the surface of a marine propeller when the ship advances with high speed cause the decline of the propeller’s performance and/or damages (erosions) to the propeller. Therefore, better understandings of the cavitation formations and the ability to predict them are important to a successful propeller design. This paper presents image results of cavitation incurred on the suction surfaces of a specific propeller and analyzes these images to obtain the statistical parameters of cavitations such as their sizes, locations, and occupied areas. These experimental results are used to evaluate the accuracy of the associated RANS simulations in order to identify issues of turbulence and cavitation models commonly used in such simulations. KEY WORDS: marine propeller; cavitation; image processing and analysis; RANS.
A numerical study of steady and unsteady cavitation on a 2d hydrofoil
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ABSTRACT: The steady and unsteady cavitation phenomena on a 2D NACA0015 hydrofoil predicted by the multiphase RANS code FLUENT are studied in this paper. Besides a numerical sensitivity study of the non-cavitating condition, the present investigation focuses on two cavitation numbers: 1.6σ = (steady cavitating flow) and 1.0σ = (with dynamic shedding). With a modified SST k ω− turbulence model, a periodic shedding is revealed: the main sheet cavity breaks up by the re-entrant jet and a cloudy cavity forms and is convected with the downstream flow. Finally, the experience with FLUENT has been used to discuss the general ability of multiphase RANS codes to predict the cavitation erosion risk. KEY WORDS: NACA0015; modified SST k ω− model; shedding; re-entrant jet; erosion risk
Research on the gas-leakage rate of unsteady ventilated supercavity *
Wang Zou 1* , Kai-ping Yu 1* , Xiao-hui Wan 2
The School of Astronautics, Harbin Institute of Technology Harbin, China
* E-mail: [email protected][email protected] ABSTRACT: The mechanism of gas-leakage is a basic problem of the unsteady ventilated supercavitation theory. This paper is devoted to the problem and presents a calculation formula of gas-leakage rate. The rate of volume change of supercavity is numerically calculated based on Logvinovich’s Principle and the empirical formula. The dimensionless gas-leakage rate formula is established by the nonlinear least square method based on the mass balance equation of gas. The formula and the existing quasistationary formula are respectively used to simulate the unsteady supercavity. The simulations are compared with the results from experiment. The result demonstrates that the formula is effective.
LES of unsteady cavitation on the delft twisted foil
Nai-xian Lu* , Rickard E. Bensow, Göran Bark
Department of Shipping and Marine Technology, Chalmers University of TechnologyGöteborg, Sweden * E-mail: [email protected]
ABSTRACT: In this paper, the cavitating flow around the Delft twisted hydrofoil with unsteady inflow condition is numerically simulated using Large Eddy Simulation in combination with a volume of fluid implementation to capture the liquid-vapor interface and Kunz’s model for the mass transfer between the phases. Main cavitation mechanisms, including periodic shedding of main and secondary cavities, side- and re-entrant jets, as well as the cavity extent and the lock-in effect between the inflow variation and the cavity are compared with experimental observations.
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ABSTRACT: Numerical simulations of cavitating flows on 2D NACA0015 hydrofoils with and without obstacle are performed. Cavitation model is based on a transfer equation for a void mass fraction and an improved RNG k-ε model is adopted to study the turbulent cavitating flows around the foils. Different arrangements and geometric parameters of the obstacles are investigated. Computational results show that cloud cavitation can be reduced effectively by an obstacle placed on the foil surface; also the performance of the hydrofoil is changed by the obstacle simultaneously. KEY WORDS: Cavitation; Re-entrant jet; NACA0015; Obstacle; Multiphase
A cavitation model for cavtating flow simulations
Biao Huang, Guo-yu Wang *, Hai-tao Yuan School of Mechanical and Vehicular Engineering, Beijing Institute of Technology, Beijing, China
* E-mail: [email protected] ABSTRACT: The numerical simulation closures for cavitating flows are addressed. Several cavitation models are evaluated with the experimental results. Based on evaluation and the analysis of the unsteady characteristics of cavitating flows, a density modify based cavitation model for cavitating flow computations is proposed, which concerns multi-phase and time scale information of the cavitating flows. Series calculations of cavitating flows with different cavitation models around an axisymmetric cylindrical object and a Clark-Y hydrofoil are conducted. The cloud cavities, pressure distributions have been obtained and compared with experimental ones. Here, differences are observed in the simulated results, due to the differences in compressibility characteristics handled by each model. And compared with the other closure models, a significant improvement for the numerical results of cavitating flows have been obtained with the present proposed model. KEY WORDS: Cavitation model; Unsteady cavitating flows
Similarity law of flowrate for hot-gas ventilated supercavity flows
Jiu-xi Chen 1*, 1 China Ship Scientific Research Center, Wuxi, China
* E-mail: [email protected] ABSTRACT : Based on the complete sets of similarity criteria for modelling experiments of exhausted-hot gas ventilated supercavity flows which had been derived by author before, considering the effects of phase changes, a similarity law of flowrate for ventilated hot-gas supercavity flows is found and described in this paper. The effects of phase changes on modelling scheme and ventilated-gas flowrate are studied. The phase changes are the vaporization of liquid water on cavity wall, and condensation of vapor contained in the flows of gaseous mixture within cavity KEY WORDS: supercavity flows, similarity, phase changes, modelling experiment
On the influence of viscous effects on 2-D cavitating vortices
Johan Bosschers
MARIN, Maritime Research Institute Netherlands Wageningen, The Netherlands Email: [email protected]
ABSTRACT : This paper describes the influence of viscous effects on an axisymmetric cavitating vortex in 2-D viscous incompressible flow in steady and unsteady conditions. A computational model is presented that solves for the cavity motion and the circumferential velocity distribution. Results are shown for the relation between cavity radius and cavitation number for steady flow including a comparison with experimental data. Unsteady simulations show that viscous effects have an influence on the resonance frequency of the cavitating vortex and show how the vortex cavity and circumferential velocity behave when subjected to a pressure change. KEY WORDS: Cavitation; vortex; viscosity.
ABSTRACT: The three-dimensional hydroelasticity theory of ships[1-3] was extended to include the effect of fluid compressibility. This enables the acoustic responses of a ship structure induced by the machinery or wave excitations being predicted with the inclusion of the free surface and the forward speed effect. A method for eliminating the irregular frequencies in the numerical analysis is proposed. The acoustic radiation of an elastic spherical shell was predicted and compared with analytical solution for validation. Illustrated in this paper are also the acoustic radiations of a submerged ring-stiffened cylindrical hull in the near field and far field. KEY WORDS: Hydroelasticity; acoustic medium; free surface; forward speed; irregular frequency.
Cavitation inception in quiescent and co-flow nozzle jets
William A. Straka*, Richard S. Meyer, Arnold A. Fontaine, Joseph P. Welz
Applied Research Laboratory, The Pennsylvania State University State College, PA, USA
ABSTRACT: The prediction and scaling of cavitation inception in jets remains a difficult task. This paper presents findings of an experimental investigation to study the cavitation inception of quiescent and co-flow submerged jets. Experimental data were collected in the ARL/PSU 12-inch and 48-inch Diameter Water Tunnels. A submerged nozzle was mounted axially along the centerline of the test section with jet mass flow supplied using an external pump. The setup allowed for independent control of both jet and freestream velocities. Observations of cavitation patterns, inception locations and cavitation inception numbers for quiescent (VR=V∞/Vjet=0), near-quiescent (0<VR<0.1) and co-flow (VR>0.1) operating conditions were recorded. Data were measured using two- 25.4mm and one- 101.6mm diameter axisymmetric nozzles. Visual observations of cavitation indicated that the cavitation occurs in different location for co-flow jets compared to quiescent jets. PIV measurements show that different flow mechanisms are responsible for this cavitation inception. KEY WORDS: Cavitation; inception; co-flow nozzle; jet cavitation
An iteratively coupled solution of the cavitating flow on marine propellers using BEM
J. Baltazar* , J.A.C. Falcão de Campos
Marine Environment and Technology Center (MARETEC) Department of Mechanical Engineering, Instituto Superior Técnico (IST), Lisbon, Portugal
ABSTRACT: An iteratively coupled solution method for the calculation of the cavitating potential flow on propellers with a potential based Boundary Element Method is investigated. By separately treating the perturbation due to the cavity a reduced system of equations is derived for successive approximations to the cavity source strength. The system is iteratively coupled to the complete cavitating system in the cavity planform iterartion. The advantage is that the cavitating system matrix is identical to the matrix of the wetted flow problem and needs only to be inverted once, avoiding new matrix inversions at each iteration steps in the cavity planform. The numerical studies are carried out for the MARIN S-Propeller and the INSEAN E779A propeller. KEY WORDS: Boundary Element Method; Marine Propellers; Partial Cavitation; Iteratively Coupled Solution Method.
Numerical study on oil and water two-phase flow in a cylindrical cyclone
ABSTRACT : Although traditional hydrocyclones are widely used in industries, there are few studies on cylindrical hydrocyclone. In this work, Euler-Euler multiphase approach and the Reynolds stress turbulence model (RSM) are applied to simulate the flow field characteristic of cylindrical cyclone. The result shows that a low pressure zone is formed in the inner part of cyclone and causes an upward flow. Velocity components distribution, tangential velocity, axial velocity and radial velocity have been calculated to study the effect of oil-water separation efficiency of cylindrical cyclone under the conditions of different flow split-ratio and non-dimensional separation acceleration. These results are helpful to design a separator system in the oil production. KEY WORDS: cylindrical cyclone; oil-water flow; split-ratio; separation efficiency.
Direct numerical simulation of collective bubble behavior
Yu-ning Zhang, Sheng-cai Li *
School of engineering, Warwick University, Coventry, UK CV4 7AL *Email: [email protected]
ABSTRACT: The present paper studied the nonlinear collective bubble behavior using direct numerical simulation (DNS) coupled with front tracking method. The bubbles inside cloud are deformable according to surrounding environment. The effects of viscosity and bubble-bubble interaction have been considered in the simulations. Response of bubble cloud with large void fraction (1%-25%) to continuous pressure wave with finite amplitudes has been simulated. A collective bubble behavior and associated pressure oscillation have been revealed from the simulations. Strong shape oscillations including jet formations of bubbles have also been observed when a strong pressure wave is passing through the bubble cloud. KEY WORDS: direct numerical simulation, cavitation resonance, bubble cloud, volume oscillation, shape oscillation, front tracking, pressure wave.
Study of ventilated cavity morphology
in different gas leakage regime
Foundation item: Supported by the National Natural Science Foundation of China (No: 10832007) and Supported by Shanghai Leading Academic Discipline Project (Project No. B206).
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Jian-hong Guo 1*, Chuan-jing Lu 1,2, Ying Chen 1 , Jia-yi Cao 1 1Department of engineering mechanics, School of Naval Architecture, Ocean and Civil Engineering,
Shanghai Jiaotong University, Shanghai, Cina 2State Key Laboratory of Ocean Engineering, Shanghai , China
ABSTRACT: Based on a suite of CFD code, a homogeneous, multiphase, Reynolds averaged Navier-Stokes solver coupled with a transport cavitation model and a local linear low-Reynolds-number k ε− turbulence model closure was used to simulate the ventilated cavitating flows around a wedge hydrofoil. The gas leakage regimes at the aft of ventilated cavities were investigated. Three gas leakage regimes were observed, and corresponding to each regime, ventilated cavities exhibited a different morphology. The numerical results were compared to corresponding experimental results in qualitative manner. It was found that the general characteristics of the gas leakage regimes and cavity morphology were very reasonably predicted. KEY WORDS: Numerical simulation; multiphase flow; ventilated cavity; gas leakage regime
Dwarf solitary waves and low tsunamis
Sunao Murashige1* , Theodore Yaotsu Wu2 1School of Systems Information Science, Future University Hakodate
Hakodate, Hokkaido,Japan 2Engineering and Applied Science, California Institute of Technology
ABSTRACT: This work applies the regularized solitary wave theory to develop accurate computational method for evaluating the dwarf solitary waves, with amplitude-to-water depth ratio 210−≤α , as a useful model of one-dimensional tsunamis propagating in the open ocean. The algebraic branch singularities of these solitary waves magnifying with diminishing wave amplitude, making their computations insurmountable by existing methods, are removed by the regularized coordinates given by this new theory. Numerical examples show that this new method can produce accurate results even for 310−≅α or less. KEY WORDS: Regularized solitary wave theory; one-dimensional tsunami waves; flow singularities; conformal mapping; numerical computation.
Examination on low-frequency QTF of a platform
Bin Teng 1*, Pei-wen Cong 1, Ying Gou 1
1 State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian 116024, China
ABSTRACT: For deep water offshore structures, the second order different frequency force may induce large responses in the horizontal directions. The second order different frequency force is usually computed by the Fourier transformation of the second order quadratic transform function (QTF), which is hard to be obtained due to its complexity, time consuming and the influence of ‘irregular frequency’ in its computation. In practical application Newman’s approximation[5] is widely used, without considering its viability. Based on a higher-order boundary element method, a numerical model is established for complex solution of second-order diffractions and radiations at different frequencies in bichromatic incident waves. The second-order quadratic transform functions are obtained by the integration of second-order fluid pressure on the body surface. With application of Teng et al’s method[9], full QTF’s are computed for a typical TLP model ISSC. Computation shows that the second-order quadratic functions have distinct distribution at lower frequency ranges. Comparisons are made on the Newman’s approximation with the full difference-frequency QTF.
ABSTRACT: A numerical time domain simulation model has been developed to study the highly nonlinear interactions between waves and rubble mound breakwaters. In this model, a volume of fluid (VOF) technique is used to capture the violent free surface motion. The incompressible Euler/Navier-Stokes equations, written in an arbitrary Lagrangian-Eulerian (ALE) frame, are solved using projection schemes and a finite element method on unstructured grids. A general advancing front technique for filling space with arbitrary separated objects is developed to model the rubbles that are laid down on the sloped surface of the breakwater in a random way. Three case studies are performed to study the effects of rubbles and rubble types on the wave dissipation and wave overtopping. KEY WORDS: Wave-body interaction; Rubble mound breakwaters; VOF; FEM; Overtopping; Grid generation.
Numerical simulation of wave transformation incorporating porous media wave absorber
Jie-min Zhan 1*, Zhi Dong 1,2, Yi Han 1, Wei Jiang 2 1Department of Applied Mechanics and Engineering, Sun Yat-sen University,
Guangzhou, China 2Guangdong Provincial Research Institute of Water Resources and Hydropower,
ABSTRACT: Wave propagation over arbitrary depth and interaction with structures are of fundamental importance in coastal and ocean engineering. Accurate numerical simulations providing more detailed information than physical experiments can enhance the understanding of such problems. Early numerical studies are mostly based on potential flow theory and shallow water equations, in which the fluid viscous is not taken into account. Recently with the development of computer technology and CFD methods, it is desirable to directly solve the Navier-Stokes equation. In this paper, a numerical wave tank is established with the classical Navier-Stokes equations and the VOF method. An effective numerical method for wave absorbing utilizing the energy-dissipating property of porous media is proposed. The applicability of the presented viscous models is assessed in detail through the two test cases of wave diffraction around a semi-infinite breakwater and wave focusing by bottom topography. The computed results agree well with experimental data. KEY WORDS: Wave transformation; porous absorber; VOF model
Numerical simulation of wave impact on the slab
Ya-mei Lan 1*, Wen-hua Guo 2, Hua Liu 3, Qiu-hong Song 1, Jun-ting Yuan 1 1 College of Engineering Science & Technology, Shanghai Ocean University, Shanghai, China
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* E-mail: [email protected] 2 Estuarne & Coastal Science Research Center, Shanghai, China
3 Shanghai Jiao Tong University, Shanghai, China
ABSTRACT: In the paper, the wave generating and absorbing were introduced into the RANS equations as the source terms using the relaxation approach. A new module of the wave generating and absorbing function, which is suitable for FLUENT based on the volume of fluid method (VOF), was established. The computational results of the wave pressures on the bottom of the slab were validated for the different relative clearance by the experimental data. Good agreements were found. It is suggested that the numerical wave flume is capable of simulating the phenomenon of wave impact, especially the process of the negative pressure. KEY WORDS: VOF method; wave generating and absorbing; numerical wave flume; slab
Development and application of high order Boussinesq model in tsunami studies
Hua Liu 1* , Xi Zhao 1 , Ben-long Wang 1 1Department of Engineering Mechanics, Shanghai Jiao Tong University
ABSTRACT: The recent progress in development and application of the High order Boussinesq-type equations for numerical simulation of tsunamis is presented. The moving bottom is implemented to simulate the generation of tsunami induced by submarine earthquakes. The wave patterns of tsunami near the source are obtained for the cases of different magnitude of earthquake and the depth of ocean, which confirms that the leading depression N-wave occurs when the earthquake magnitude is large enough. The numerical model is applied in modeling the India Ocean Tsunami in 2004. The computed value of the runup of tsunami is compared with the data from field survey available. KEY WORDS: Boussinesq equations; tsunami; solitary wave; N-wave; runup
Hydrodynamics of coupled river-lake system
Lin-lin Li 1 , Xi-ping Yu 2*
1Earth Observatory of Singapore, Nangyang Technological University, Singapore 2Department of Hydraulic Engineering, Tsinghua University, Beijing, China
ABSTRACT: A numerical model based on the finite difference solution of Saint-Venant equation for one-dimensional unsteady river flows and the shallow water equation for vertically integrated two-dimensional flows in the lake is employed to study the propagation of flood waves in Jingjiang River and Dongting Lake. Three different types of flood occurred in 1996, 1999 and 2002, respectively, are computed. All numerical results are shown in fairly good agreement with observed data. KEY WORDS: Coupled river-lake system; Yangtze River; Dongting Lake; Hydrodynamics; Numerical model
Large-eddy simulation of stratification effects on dispersion in urban environments
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Zheng-tong Xie *
1School of Engineering Sciences, University of Southampton Southampton, UK
* E-mail: [email protected] ABSTRACT: This paper focuses on investigating thermal buoyancy effects on dispersion of approach flows and local heat transfer from/to buildings by taking the DAPPLE site as the test case but for varying wind direction and magnitude. Firstly, based on the BT tower data, only weakly unstable conditions (i.e. Richardson number |Ri|<1) of approach flows were considered, with adiabatic boundary conditions at the ground and building surfaces. It was found that the predicted concentration in the far field was significantly reduced. Secondly, numerical experiments were performed, i.e. using various Richardson numbers. It was found that the modelled mean concentration for bulk Richardson number -0.9 was in reasonable agreement with field data at all stations. Thirdly, to understand the effects of weakly local unstable conditions, non-adiabatic boundary conditions at ground and building surfaces were implemented as well as weakly unstable conditions in the approach flows. No significant difference was found comparing with those using adiabatic boundary conditions. These simulations suggest that stratification effects on dispersion in weakly unstable conditions (e.g. in London) are not negligible.
ABSTRACT : Jet flow is a very important research subject in both fundamental fluid dynamics and engineering applications. Jet flow has the essences of fluid dynamics, such as free and wall-bounded shear flows, turbulent flow, eddy and large vortical structures and their stability and control, and so forth. This article serves as an overview of our past and ongoing research activities on various types of jet flow, with particular reference to their application in the field of environmental fluid dynamics. The research objectives, approach, results and their engineering implications of each topic will be presented. KEY WORDS: jet flow, flow control, vortices
An unstructured grid hydrodynamic and sediment transport model for Changjiang Estuary∗
Ding-man Qi 1*, Gang-feng Ma 2, Feng-feng Gu 1 , Lin Mou 3
1. Estuarine and Coastal Scientific Research Center, Shanghai 201201, China 2. Center for Applied Coastal Research, University of Delaware, Newark, DE 19716, USA
3．National Marine Data & Information Service , No. 93 Liuwei Road, Tianjin 300171,China
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ABSTRACT: An unstructured grid hydrodynamic and sediment transport model for Changjiang Estuary is developed in the current paper. The model employs finite volume method to discretize the governing equations. Semi-implicit method originally developed by Casulli is utilized to remove the stability limitations associated with the surface gravity wave. A wetting and drying (WAD) scheme is proposed to account for the moving boundary at the shoals and tidal flats. The model is used to investigate the hydrodynamics and sediment transport in the Changjiang Estuary. Comparisons with the measured data show that the model can predict water level and tidal current very well. The variations of sediment concentration are also reasonably captured by the model. KEY WORDS: Unstructured Grid, Finite Volume Method, Changjiang Estuary
Research on the hydraulic characteristics of gap closing with large framed cages
Yong-jin Lu, Xiao-tao Du
Shanghai Water Engineering Design & Research Institute Shanghai, China
E-mail: [email protected] ABSTRACT: Gap closing under high current velocity is a Gordian knot in water conservancy project, jackstone gap closing with large frame cages is a new technology to solve this problem. Associated with practice in the project of Qingcaosha reservoir and analysis on hydraulic numerical simulation and physical experiment, several hydraulic characteristic rules of this technology were discovered, it is of instructional value in practices of similar projects. KEY WORDS: closure gap; closure technology; framed cage for gap closing; hydraulic characteristic; tidal estuary
Unsteady behaviors of two moving bodies through inviscid unbounded liquid
Run Sun *, Hong-yu Ma
Department of Engineering Mechanics, Shanghai Jiao Tong University Shanghai, China
ABSTRACT: We account both bodies and liquid as a conservative system to explore unsteady motions of two bodies, adopting the Lagrange equation of motion in vector form. Theoretical analysis and numerical results reveal that as two circles initially revolving around each other in an inviscid liquid with a stationary centroid are set to translate, their centroidal trajectory is sinuous and would gradually deviate from the original moving direction. For the rectilinear motion of the bodies in tandem, Galilean relativity is invalid for just two bodies during the hydrodynamic interaction, and their centroid, after initially set in motion, may accelerate and then decelerate, finally approaching a constant speed as far apart from each other. KEY WORDS: Unsteady motion; added mass; two bodies; hydrodynamic interactions.
Studies of hydrodynamics in fishlike swimming propulsion
Xi-yun Lu 1*, Xie-zheng Yin 1, Ji-ming Yang 1 , Bing-gang Tong 1,2 1 Department of Modern Mechanics, University of Science and Technology of China, Hefei, China
2 Department of Physics, Graduate University of the Chinese Academy of Sciences, Beijing , China * E-mail: [email protected]
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ABSTRACT : In this paper, we will attempt to provide an overview on the hydrodynamics of fishlike swimming propulsion based on our recent work performed experimentally, numerically and theoretically. We mainly present some typical work, including measurement on kinematics of free-swimming fish and prediction of dynamics acting on an arbitrarily deformable body, numerical and experimental simulations of flow over flapping and traveling wavy bodies, and the relevant biomimetic technology.
ABSTRACT: The use of newly available tools in propeller design is discussed. It is stated that new tools are too much used to imitate experimental results. The paper takes a step back and investigates new approaches to ship propeller design in which new tools are better integrated or calibrated. KEY WORDS: Propeller design ; cavitation; model test.
On the evolution and run-up of tsunamis
P. A. Madsen 1* 1Dept. of Mechanical Engineering, Technical University of Denmark, Lyngby, Denmark
ABSTRACT: The first part of this work investigates the validity of the classical solitry wave paradigm for tsunamis. Our study involves the evolution of transient waves, from the initial release of a hump of water, then propagating large distances over flat bottom and finally shoaling over a mildly sloping bottom from the ocean to the beach. We monitor the development of time- and space-scales and compare with solitary wave theory. Next, we simulate the disintegration of long waves into a train of undular bores and discuss the relevance of this phenomenon for tsunami runup. We conclude that solitary wave theory is not applicable for geophysical tsunamis. In the second part of this work, we derive new analytical run-up formulas for incoming single waves and leading depression N-waves, where the time- and space-scales can be chosen freely independent of the wave height. Finally, we derive a convolution formulation for the run-up of transient waves. This is compared with a numerical simulation and the results are in good agreement.
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ABSTRACT: As a long-term hydrodynamic phenomenon induced by waves, the currents dominate the pollutant transport in the shoaling and surf zones. The present study was focused on the analysis of the cross-shore currents induced by waves and the pollutant transport. The wave parameters were obtained by solving one phase-averaged wave model including wave shoaling and breaking in the surf zone. The effect of the breaking wave rollers in the surf zone was considered by specifying an additional boundary condition on the mean water level (MWL). We introduced a formula for the vertical varied wave radiation stress into the hydrodynamic model. Furtherly, we simulated and analyzed the pollutant transport in the domain for different pollutant release position. KEY WORDS: undertow simulation; vertical varied radiation stress; surf zone; water quali
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